I had a problem with enemy territory with 2.6 as well, but I don't think it's nvidia related, (could be though, who knows)
Everything went smooth upgrading to 2.6 except enemy territory maps would take longer and longer to load.
With lin 2.4 on my system (p4 1.6 gf4 ti 4200 128 megs of ram) it would usually take about 30-40 secs to load a map. I know I'm kinda low on ram but it would usually work fine. With 2.6 the first map would take about the same time, 30-40 secs, but each map thereafter would get longer and longer, around the 3rd map would take over 3 minutes and I'd get kicked from the server.
I even try hosting my own server as a test, just kept reloading the same map, and the map load times just kept getting longer and longer. From 30 secs to over 4 minutes.
With everything else the performance would seem the same, I tested hdparm and getting about 40 megs/sec (same as 2.4). So it doesn't seem to be a DMA issue.
In the end I went back to 2.4 because I don't like not being able to play ET.