this is the specs I found for that computer:
So only a pci slot. And pci graphics cards suck. And if he still has 256mb ram he needs to upgrade it. It would be smart to go for the 1GB (max supported by the mobo)
But I'd just built a new computer. If he wants to play BF2 he needs to upgrade the ram, probably the mobo (and I don't think that u will find any good mobos for that socket, so maybe the processor too), the psu and the graphics card.
So u would be left with the case and maybe the processor. U can use the old processor if u like, but I'd get an socket 939 amd cpu.