I have had a similar problem with my ATI Radeon 9800 Pro.
In my case, it was because the video-card didn't get enough power.
I fixed it by changing the AGP voltage from 1.5v to 1.6v...
Try it, if it works: great, else put it back to where it was.
A little bit extra voltage shouldn't hurt the card, but the lifespan might get decreased a little (like a month less
)
Tell me if it worked...
PS: Just to make sure we're on the same line, if the problem really is the heat, then this won't work (more voltage is generally more heat), but to be honest, I'm notn sure 70 degrees is considered a risk yet.. especially not under full load with BF2. I had the same problems, with games going black after a while and all that, and I tried several different cooling solutions, but in the end all that worked was to crank up the voltage