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Possible to use JqMobi for both desktop and mobile browsers?

we have a site that is running on Jquery and Backbone.
But it is rather slow on the mobile, but i do not want seperate bases for the desktop and the mobile.
I was wondering if jQmobi runs well on desktops as well? I do not care about supporting IE8 and below.

It's webkit only, so if you only care about Chrome/Safari it works fine, but it does not work on FF/Opera/IE currently.
note (I'm the lead dev. I use Chrome desktop for development then test on device)

How to Draw lines using wz_jsgraphics.js library in IE 7/8/9

I am using wz_jsgraphics.js library to draw lines. It is working with all browser other than IE 7/8/9. Now I want to run it on any IE7/8/9 browser. Please guide me to resolve this problem.

Walter Zorn's wz_jsgraphics.js works fine in IE7, IE8, and IE9 when I use these browsers on four different computers.
Internet Explorer has quite many options. Maybe one of them needs to be changed on your computer. For instance, if you are running jsgraphics offline from an html document on a file, the advanced IE option Allow Active Content To Run From A File (or whatever it is called) must, of course, be checked.

JS library to simulate Internet Explorer?

There are some JS library to simulate the IE in Webkit? For instance: IE8 doesn't support border-radius currently (maybe on IE10). So I run a JS library that check if I'm using the border-radius then remove it to make similar to IE vision.
It's a crazy idea, I know, but work on IE is too slow, and if I can simulate it on Webkit, will be great! I need do it to an own project too.
Note: I know that exists a Chrome extension to make a IE tab, but the proposal is different: I need run on Webkit, but eliminating features not supported on IE.
Edit1: I'm working on a Webkit based IDE to developer HTML templates. Basically I need a button that emulate the IE view version without need a IE installed too (Mac, Linux for instance). Will be interesting have a Mozilla emulator too, for instance. Basically I will generate a CSS file to each browser too. For instance: -webkit properties not will be included to MSIE CSS. filter not will be included in Webkit CSS (but can be emulated).
So, I'll make a copy of current HTML page before apply a JS method that will edit or delete the unsupported content, make it similar to IE. If IE8 not support border-radius, it'll be removed and I'll see basically an IE version of page. If Mozilla not support -webkit-box-sizing it will be renamed to -moz-box-sizing if disponible.

I know of no script, and frankly I don't expect to see one any time soon as the task of re-creating the topography of IE's support for CSS in various versions of the browser would be a massive undertaking. It would further complicate things if the undocumented hacks like _height were supported too.
Frankly, the best way to test your site in IE8 is to use IE8+. In versions IE8 and up Microsoft introduced Browser Emulation, permitting you to fallback and emulate any number of IE versions all from a single browser - I use this daily, and it's a fantastic feature.
Within IE, open up the Developer Tools by pressing F12 and from there you can change the Browser Mode to IE8. No refresh will be necessary as the browser will handle that on its own. Using this method you can quickly test versions 7 through 10 (assuming you're testing from IE10) with the click of a button.
Disabling CSS3
If all you would like to do is disable CSS3 features, you can use the Strip Tease bookmarklet. It's not a fully-developed solution, so keep in mind that it won't handle things like advanced selectors, etc.

Drag and drop upload plugin

I want to create a jquery drag and drop file upload plugin or use an existing one.
Unfortunately I cannot find any plugin that does exactly what I want to achieve.
Can someone point me a good place to search or how to start to implement my own file upload plugin?
Thanks.
I need the following functionality:

The one should work perfectly for your needs. I have used it and it is pretty simple to configure and use.
http://valums.com/ajax-upload/
Here are the features
multiple file select, progress-bar in FF, Chrome, Safari
drag-and-drop file select in FF, Chrome
uploads are cancellable
no external dependencies
doesn't use Flash
fully working with https
keyboard support in FF, Chrome, Safari
tested in IE7,8; Firefox 3,3.6,4; Safari4,5; Chrome; Opera10.60;

also, you can try PLUpload (http://plupload.com/)
On that page you'll see that Drag&Drop is supported by HTML5, Gears(from Google) or BrowserPlus.
Note: Drag/drop support of files is currently only available in Firefox and WebKit. Safari on Windows has some strange problems and requires workaround.
In IE and/or Opera, that drag&drop could not work properly as you expected.

What are the quickest and easiest ways to ensure existing web pages display well on mobile platforms?

The pages in question contain a lot of javascript and CSS. How well are these supported by mobile platforms generally?
Is there a browser emulator (or equivalent tool) to assist testing?

Opera has an option to view pages as through a mobile device. I've found it useful in the past.

I can tell you that Apple's Mobile Safari on the iPhone renders Stack Overflow perfectly, which I find rather amazing.
This is a site for programmers, not average users, so we accepted a lot of JavaScript dependencies.
I do wish more mobile devices had browsers as powerful as Mobile Safari. I hear good things about Opera Mini as well.

One example:
The standard BlackBerry browser on my BlackBerry 8130 (Pearl) seems to ignore both CSS and JavaScript when loading my home page.
I also installed Opera Mobile on this device, which renders the CSS but not my jQuery hover effects. It does understand some jQuery - for example, I have a form validation that does a show() of error messages if validation fails. That works in Opera, although without the animation effect.
The safest thing to do for mobile browsers is to design pages that degrade gracefully without JS or CSS. It's up to you whether that's worth the effort or not.
In a few years, hopefully the only rendering differences will be the screen size limits of the phones.

You can install Opera Mini on an emulator like the Java WTK and test mobile rendering on a PC. One drawback is that Opera Mini still works through a proxy, so debugging local files/sites won't work - you have to upload your site to a world-accessible server.
Just google it.

It depends entirely on the phone. If you want to support every single device out there, don't even bother with CSS or JavaScript since neither will work (or will do something completely non-standard) on 99% of devices. If you are only targeting high-end devices, like the iPhone or the latest Series 60 Nokias, you should be able to get away with limited JS and CSS.
Some browser emulators that I know of:
Openwave.
Nokia tools
There are many more manufacturers that simply do not have any tools at all (I dare you to try and find a developer site for LG) so you need to get access to the physical handsets if you want to be sure the site appears as it should.
DeviceAnywhere is a superb tool if you have the cash. It was extremely laggy the last time I used it about a year and a half ago. Plus it is pure Java so is a dog on any machine. But it is arguably the single best mobile development tool available and, believe you me, I've tried a lot.

BlackBerry devices with OS 4.5 or older will not handle Javascript or CSS very well, if at all. Devices with OS 4.6 and higher (Bold, Pearl Flip, Storm, etc..) come with a new rendering engine which has much better support for Javascript, DOM, and CSS. It's not perfect but it should render most pages quite well. You can download the BlackBerry simulator for these devices from their developer website and try it out. Since it runs the same code as on the actual device it's an excellent representation of what you can expect to see on-device.