Computer keeps freezing

[Genesis15]

my specs are:

XFX 6600GT 8X AGP
AMD Athlon AM2 3800+ X2
2gb corsair ddr2-667
300w antec tp-II
windows xp pro sp2
k9mmv msi mobo

when playing games my computer freezes causing me to reboot, so fuck counter-strike 1.6 is fine, but hl-2 and guild wars always freezes my cpu/mobo and ram is brand new, i just formatted what could it be

 

[Genesis15]

I've been reading and I see that some people believe it's my PSU lacking... well, I have 3 psu's: Antec 300w True-Power, InWin 300W, Power Q 350w.. What do you think will be best???

 

[Genesis15]

I also see theres some confliction between VIA and AGP?? I dont know, guys I really need HELP... I've dont everything but swap parts, but my GPU was running fine before,