If you were able to run it fine on xp but it becomes choppy with large
load times in the middle of the game, it's probably due to vista's
higher memory usage. I had 1.5 gb of ram in my pc when it had xp
installed, and it ran bf2 just fine. But when I upgraded to vista,
that wasn't enough memory to run bf2, and I had large load time gaps in
the middle of the game from loading from the hard drive, even though
most game play was pretty smooth. I added another gb of ram to take it
to 2.5gb and the problem went away.
My problem is that each time i enter into a chopper or an airplane, if i
stay with the cockpit view i have no problem, the game runs fine with high
framerate, but when i switch into "full-screen" view for the chooper or the
aircraft (the view of the videocamera mounted on the top of the vehicle) for
about 30 secs the framerate drops to 8 fps, and after that time framerate
returns to 70.
BUT if you run correctly BF2 on vista, maybe it's only a problem of mine.
Did you installed AMD Dual Core Optimizer, the new release of november? Wich
is your video-card? ATI or nVidia?