Thanks for your replies! Now I'm even more confused

I composed a custom PC on alternate.de (taking a G-Force 8800GTS, without WindowsXP) that turned out to be the same than if I'd buy a complete system from Dell (taking a G-Force 8800GTX including WindowsXP)...well the Mainboard was probable a bit better than the one from Dell (does someone know what mainboard Dell uses in the Dimmension 9200??).

Hm...I might just replace the broken mainboard from my old machine and use it till the machine blows for good