So it looks like the culprit is AVG. I tried killing the (many) processes that it has running, but only a few would go away. The others said I didn't have permission to kill them, even though I was running as administrator. I uninstalled AVG completely, and BF2 worked fine after that. I re-installed AVG, and BF2 started having the same problem again.
A workaround is to temporarily disable AVG by going into Tools->Advanced Settings and checking the appropriate box. It only allows you to do this for 15 minutes max, but I found that if kicked back on while the game was running, it didn't have much of an impact on performance.
Wow. You just made me feel very nostalgic with those specs.
Okay, I wish I could stop saying this. Just because one game runs fine doesn't mean the other does!
Just because it used to work doesn't mean it still will. I know it says "minimum 1.5ghz pentium 3" But that means with the utterly lowest settings. Your entire rig hits the bottom end of the Recommended settings. XP SP3 eats quite a bit more CPU than 1 and 2. AVG has also gotten more CPU intense over the last year. (Annoyingly.) Those two alone combined eat up pretty much most of your speed.
Now for possible solutions that don't involve spending money....
Does it work if you turn everything to extremely low?
Also, it is possible your pc overheats. Run GPU-Z for the GPU temperature, and CPU-Z for the CPU temperature.
Would this "minimal processes" be the ones listed under the Tasks or under the Processes tab in Taskmanager? Because most processes aren't listed in the most commonly used tab in taskmanager. Try seeing what you can shut down from the Processes tab. (Not by clicking 'end task' at random! That WILL reboot your pc!) Use google to look up what process does what before you kill it.
After I start BF2 v1.1 up, it becomes extremely choppy, even before I have selected a profile, to the point that it's hard to get the cursor to line up with a button to click.
I've followed tweak guides to use the no movies, no intro, windowed mode, and no startup music arguments on start up. It goes straight to the profile screen and seems fine at first, but after about 15 seconds it becomes choppy. CPU usage is maxed out at this point.
I'm running a Dell P4 2ghz (single core) from 2002, with 768 RAM and ATI Radeon 9800 Pro with 128 MB. Still have 8GB available on a 40 GB hard drive. Windows XP SP 3, fully updated. Minimal processes running in the background (AVG anti-virus).
Other games run fine, like Starcraft, Diablo 2, and Steam games. BF2 has run fine previously on this machine, too, but it's been a couple years since I last ran it I think.
I didn't see a search feature for the forums here, so I apologize if this is a well-known issue. Google didn't help me much, either. I appreciate any help anyone can offer!