My experience, for what it's worth, is that the single most important thing for playing BF2 properly is gobs of ram. 1GB is the MINIMUM spec to make it run even vaguely properly, 2GB makes a huge difference. It doesn't actually need the fastest possible cpu/graphics card, although obviously that will help. For instance, It works quite happily on my games box, which is a 3 year old shuttle with an XP3200+ in it, even with the original radeon 9700, at 1280x1024. Very pretty graphics indeed.

I've upgraded to a 256MB 6800GT card which made it even prettier, but it was fine before. On the other hand, only 1GB of ram meant it was swapping to disk all the time, causing the game to stutter for the first minute or so of play, and intermittently throughout the game. 2GB fixed it completely.

pca