np's my pleasure
7800 GS possible fixes;
1) Go to:
Start->control panel ->display->settings->advanced->troubleshooting->> below the hardware acceleration slider there is a box you have to untick, (enable write combining). This has been known to cause issues with some AGP cards, I used the only AGP card I have - my 6800GT to illustrate.
2)Do you have 'fast writes' turned off, it's a known cause of AGP GC issues?
3)I have seen some reports of Nvidia drivers(even the latest ones I linked you to before) causing probs with your card. I never found any real substantial evidence of this though.
4) Worst case scenario - Re-install BF2 and see if this clears things up. If it doesn't I feel that you may have a defective card and RMA is your only route. Keep us updated mate.

7800 GS possible fixes;
1) Go to:
Start->control panel ->display->settings->advanced->troubleshooting->> below the hardware acceleration slider there is a box you have to untick, (enable write combining). This has been known to cause issues with some AGP cards, I used the only AGP card I have - my 6800GT to illustrate.
2)Do you have 'fast writes' turned off, it's a known cause of AGP GC issues?
3)I have seen some reports of Nvidia drivers(even the latest ones I linked you to before) causing probs with your card. I never found any real substantial evidence of this though.
4) Worst case scenario - Re-install BF2 and see if this clears things up. If it doesn't I feel that you may have a defective card and RMA is your only route. Keep us updated mate.