Upgrading my computer....what should i get?

I've got a desktop pc with an AMD +2800 cpu, nVidia 7800 GS agp card, 2 gigs of ram, and 240 gigs of space in a 160/80 setup. Without having to spend too much money i want to upgrade, but i dont know what would be the best thing to get performance wise... My choices seem to be higher grade ram, an NIC card (network something or other, to prioritize internet transmissions), a higher grade cpu that my mobo can handle (socket a/949 i believe). I would like to avoid a new mobo as that would entail getting new everything else. A brief explanation on which part would be best and why would be a wonderful answer, thanks!