1.Should have support for standard h/w (have 1900XT, Creative X-fi).
2.Should have good looks , something which beats vista and similar to those of Apple's OS X.
3.Should support messengers (MSN, Yahoo or any other alternative).
4. Should be able to support torrent client ( prefer Azureus)
5.Should be stable (system will be crunching)
Pretty much any popular version of Linux will support all of these things. Think of Linux as modular OS, you install the software you want as you need it. Although there are many basic distinctions between Linux Distro's you can pretty much find versions of the same software for almost any popular distribution.
And unlike windows installers, Linux uses package managers like apt or yum to install software. These package managers will not install software for which you do not have correct dependencies.
It is a better idea to use a distribution that is more popular, therefore, you will have more community support, and it will be easier to troubleshoot for someone that is newer to these os's.
Some of the more popular ones
Ubuntu/Fedora/Suse/Gentoo/Mandriva/Debian/Mepis/Slackware/FreeBSD
Quite a lot of of these distributions have the availability of using a liveCD, so it is a good idea to download these distro's and run them from cd to test them and see which ones you like. In fact, you can even install many of them onto a flash drive and then boot directly into them, these are both really good ways of testing before you decide.
If there is a Linux driver available for one distro, it is pretty much available for all of them, if there is not a pre-packaged version of the driver, it can be built/compiled from the source files (in most cases) pretty easily.
Getting your hands dirty, is a must with this OS, yes it can be pretty simple in terms of pre-configuration, but do not think for a minute that you will not have to dig in and learn. The community support for most of these popular distributions, are incredible, and there is always a guru out there that is more than happy to help with questions. In most cases just going to the distro support forums, or using google will find your answer for you, and in most cases someone else has already had the same question as you.
Good luck, it a really rewarding when you have it sorted out, and I think you will find it well worth the effort :hap2:
and ya Linux drivers have released for ATI but nVIDIA has better support they keep on releasing new drivers @ regular interval of time 
hyeah:.But there are lack of drivers as far as ATI is concerned .. well you can install Drivers using Restricted Driver Manager or use Envy Script ..
You can change too but that will require some steps to save Grub Loader in Boot Loader Option wlse you will lose direct link to Linux :S That's typical leave that install Windows then Linux
