We're using the full retail version of Doom 3 patched to version 1.1 and we did a manual run through from a section of the "Alpha Labs 1" level for the purposes of our comparison. Anti-Aliasing and Anisotropic Filtering were configured from inside the game, and thus we've left the drivers set to "Application Controlled".
Due to the darkness of Doom 3, we find that increasing the resolution has greater image quality benefits than applying AA to a lower resolution.
GeForce 6600GT AGP:
The GeForce 6600GT was capable of delivering a playable frame rate at 1280x1024 with 2xAA 8xAF with the in-game detail settings set at High Quality. Unfortunately, due to the GeForce 6600GT only having a 128MB frame buffer, we were unable to run at 1600x1200 without Anti-Aliasing because of the possible lack of fill-rate or memory bandwidth provided by this video card - the minimum frame rates dropped to unacceptable levels.
ATI Radeon 9800 Pro:
On the other hand, ATI's Radeon 9800 Pro, the GeForce 6600GT's current mid-range competition on AGP, was capable of delivering solid frame rates at 1024x768 with 8xAF with the in-game details set to High Quality. The Radeon 9800 Pro lacks the memory bandwidth to be able to run with high-resolutions, along with the fact that the GeForce 6 series has exceptional performance in Doom 3.
Aside from the increase in resolution, we see differences in the quality of the grid floor, with the GeForce 6600GT providing superior image quality in that section of the scene - this was the case across all grided areas. There are the 2xAA white speckles that we have pointed out in both Catalyst 4.10 and ForceWare 66.81 - it appears that the speckles are down to a game issue, and not a driver issue.
Using 2xAA doesn't completely eliminate the jaggies on the railings, but it does help to reduce them, it is clear to see that the jaggies aren't quite as harsh in the screen grab from the GeForce 6600GT.
Both video cards deliver a very solid frame rate, with the Radeon 9800 Pro providing the highest minimum frame rate. However, we must remember that the two video cards are running completely different resolutions, and the GeForce 6600GT is the better performer in this title, by quite a large margin. The Radeon 9800's lack of performance could be due to the fact that the core logic does not include support for ATI's anisotropic optimisations that appeared in the Radeon 9600 series, and now feature in all of the X series video cards.