Hi...You dont have to check the compatabilty of the vRAM and the mobo...The factor that you should check is the Slot type...Whether the mobo has PCIe x16 Slot or AGP slot for choosing the graphics card type...
If you have a PCIe x16 slot, then you can use any PCIe x16/ PCIe x16 2.0 Graphics card and vice - versa
If you have an AGP slot on the mobo, then you can use only AGP graphics cards...
Your mobo has PCIe 2.0 slot so it can use any of the PCIe x16/ PCIe x16 2.0 cards with any type of RAM be it GDDR3/ GDDR2/ GDDR5/ or any...
So just check the slot type...
And your mobo is compatible with that card...
A general suggestion though...that 9800GT card is not worth that money...
Instead get this...
http://www.newegg.com/Product/Product.aspx?Item=N82E16814130469
And before you buy these discrete graphics cards, check if your power supply will be able to handle these...