Another gig of ram is all you need for BF2. I had an amd 3000+, x800 bravo and 2 gig of cheap ram and I ran it maxed out at 1024x768. It ran perfectly, but i've yet to see how much more perfect it will be with my new 8800gts.
Having 2 gig of ram also lets you alt+tab out of it without killing your computer, and you can do stuff as soon as you close BF2 rather than waiting 15 minutes for the computer to sort itself out.
What are the specs for BF2142 btw, basically the same as BF2?