Get the latest driver for your graphics card if you don't have it.
http://www.nvidia.com/object/winxp_2k_81.98.html
I have the same 7800 GTX 256 MB showing 256 for memory, which is correct.
Finding out the driver version of your display card, follow this steps.
Click start
Go to My Computer and right click then to to Properties.
You'll see System Properties
Click on Hardware and go to Device Manager which pops another window
In the Device Manager window find the icon that says Display adapter and click
On either card right click and go to properties, which pops a another window saying Nvidia GeForce 7800 GTX Properties
Click on the Driver Tab
You'll see the Driver Version displaying your current driver for the graphics card
The latest one should be the 8.1.9.8 version.
If not then update it.