win2k3 is basically the same thing as XP.
Main difference is extra security enchancements and server utilities.
However there are many tutorials on setting it up for use as a desktop os(including for playing games like cs ;)).
But it is important to remember that you don't need a server os to run a 'server'. All you need is the proper daemons for the services you'd like to offer.(FTP,HTTP,SMTP,POP3,ETC)