1.5gig is the minimum for good performance in BF2 unless you sacrifice something on visuals. Lots of people claim it is 'fine' with only 1gig, but that's because they don't know any better.
Other games such as FEAR, WoW, Boiling Point and Freespace 2 all benefit from over 1gig of RAM.
Personally I'm struggling along with 1gig RAM because I don't play many games with such hefty memory requirements, and I tend to run very few background tasks. I'd prefer more memory of course but my current sticks run at 231mhz CAS2 which is hard to get from a value 2gig set. I can live with the fact that some games will have longer load times and occasional paging, or I have to use reduced texture settings - but that doesn't mean I'm not aware that 1gig is definitely sub-optimal in the current day and age.