You can host the game on the server for everyone to play on, but you will need another machine for yourself to play with them.

Besides if you were to play the game on the server that would be cheating.... since your ping would be 0 (zero).

you will have to install XP or Win7 to do what you want ( and it would still be giving you an unfair advantage )

Well first thing you need to understand is that Server 2003 is NOT a normal operating system!  It's a SERVER.
Second, AMD/ATI do not support their gaming cards (yours) in a server environment.
Third, as far as I know DirectX can't be installed in a server environment.  So even IF you managed to get the XP drivers to work, you wouldn't be able to play any modern game anyway.

Get with the times and install Win7.  You'll be MUCH happier.

I want to use the server to play games, with friends, to install a certain game on the server and to play it together with them, at the same time (real time), using the same profile. Is that even possible with Windows Server 2003 ?
I'm sorry for asking that kind of questions, I know they're a bit off-topic, but I'll still be grateful if you reply.

Get with the times and install Win7.  You'll be MUCH happier.