Hi
regarding your build, it very much depends on what you have to spend. If you post your list in the "new build" section im sure someone will advise on componants. For a gaming system, these are my basic opinions.
AMD processors are considered the best for gaming. Go for an Athlon 64, anything beyond 3000+
Get AT LEAST 1gb of ram (corsair is a good brand), more if you can afford. BF2 gets very memory hungry.
For your AMD 64, get a Motherboard that supports Socket939 Processors, and PCI-Express graphics. This is the new technology that will help with future upgrades. Gigabyte, ASUS, and ABIT are good choices.
Get as strong a graphics card as you can. an Nvidia 6600GT is good, a 6800GT better if you can afford.
Just a few basics to get you started
Freakitchen