I'm using Linux only at home as desktop and quite happy with it. MS Windows was removed permanently!!!
I use Fedora Core 3 - it nice easy to install. I've tryed also Debian Sarge it is very good also but it more professional oriented system and more complex in installation. Others Suse, Mandrake hadn't tryed. Ubuntoo - is Debian based.
Fedora Core 4 - is very new and it is testing version... So unless you want newest soft, but less stable you can try it.
MiniD - what apps will you be able to run on your Linux system?
Internet - Mozilla, Fireforx, Mail
Open Office - Word, Presentation, Spreed Sheet (quite compatable with MS one MS Word, Power Point)
Gimp - powerfull photo editor
Various Servers and net applications, Lot of developlent tools.
Multimedia - movies, music etc...
Lots of other great free opensource software.
You have usually the very good package that is given with the distribution and you can download much more!!!
You can do all that you have in Windows!!!
Accept playing games - AH2
If you install Fedore there is number of very usefull links:
http://www.fedoraforum.org/ http://www.fedorafaq.org/ This FAQ must to read - gives lot of important things for you. How to install multimedia, get all you need working.
I'm going to be working on a project with my GF (tomato) to develop a Linux box with a view to seeing how far we can push it with regard to running Windows applications and using it for games.
In order to run Win Apps you will need WINE. Usually each distribution has one. I don't know if it is same for 64bits (there are no 64 windows now only very first betha version... Actually all windows versions are bethas)
You probably need for these
WineX - DirectX support for Linux - in order to run windows games,