Choice of OS

[Awwent]

I need help to choose an OS for my server.
I have an Athlon64 X2 Dual-Core 3.0GHz and 2GB RAM (going to upgrade to 4GB RAM) and a Western Digital Raptor 36GB with 10 000 RPM.
Windows Server 2008?
Windows Server 2003?
Windows XP?
Linux?

[Awwent]

EDIT: I do not want Linux, please. I'm used with Windows and I think it's a lot easier than Linux, and I think it's more effective.

[Hazz]

Windows server 2003 if you are happy with no more than 500FPS.

Windows 2008 if you want more that 500FPS.

[Saturnsix]

but there is a trick you need to do before you enable it with windows 2008 for 1000fps