Problems with XP and computer gaming...

[All Hallows Eve]

I'd like some help with my setup. I'm running an Athlon 64 bit 3200+ on an MSI K8N neo4 mobo. I have a Geforce 256meg 6600gt graphics card and 1 gig of RAM. I also have a SATA 120 gig and Windows XP professional installed.
I tried to install service packs for the OS but the OS restarts whenever booted with them installed so I rolled them back and installed the latest graphics drivers and tried again to no avail. I didn't think much of it until I couldn't use WMP which isn't a big deal in itself but still probably part of the problem. I reinstalled Windows XP and it still had the same problem. The problem also occurs when I try to play games like half life 2 and Xpand rally. Games with high graphic detail, however other games work fine.
I'm totally dumbfounded by this problem as it seems like software and device drivers do not want to play nicely with each other I just don't know why.
Any help would be greatly appriciated.

 

[NeuromancerWGDD'U]

For the games, have you tried installing the latest version of DirectX (the WMP problems lead me to believe it might be a DirectX issue. What does it do when you try to start WMP?)? Also, I myself have a SATA drive, and I can tell you, both XP and Linux don't want to play nice with it, so you might want to check and make sure that the service packs don't require extra steps to deal with SATA.

 

[All Hallows Eve]

My directx version is up to date as far as I'm aware. I installed WMP version 9 over the version that comes with windows but it used to just make a ding and not do anything afterwards, no error logs or anything would pop up on screen.
Well I had my OS installed on a 20 gig IDE hd but the same problems occured when using it, I transferred over to the 120 gig because the 20 was just too slow.
Any other thoughts?