Itll fit fine on either PCI-e slot, but itll take up one PCI slot on the lower one.
Also make sure you get eVga and when you register it, you will have a 90 day period for when you can upgrade it and pay the difference of the new card. DX10 cards should come out within that period.
AMD X2 4200 + Zalman 9500
Asus A8R32 MVP Deluxe Motherboard
eVga 7900Gt Ko + Vf700 @ 600/1620
SB X-Fi XtremeMusic + Klipsch PM 5.1
Thermaltake ToughPower 750w Modular
Seagate Barracude SataIII 250Gb
Samsung/Lite On Dvd/Cd RW
NEC 20WMGX 20\'1 WideScreen
ThermalTake Tsunami Case