Indeed, you can go crazy expensive on a computer but it will gain you nothing. For a computer to play everything at max and continue to do so for a good few years is likely $2000 and even that will likely be over the top of what you need. Sp12 has it about right
if i buy all the top of the line items for everything, how much would that cost me?
Well over $9000.
Buying a new graphics card, something relatively cheap compared to a top of the line computer, like the $200 GTX 460 would be able to run SC2 at maximum settings without any problems. Your CPU is good.
Make sure you have 4gb of RAM and get a better GPU - 5770 at least, GTX 460 (1gb) or a 5850 (on higher end of budget).
The 5770 should deal with SC2 no problem, i you play other games you may find the extra money spend on a GTX 460 worthwhile, if you play lots of games then the 5850 is worth the buy if you can afford it.
If your motherboard can Crossfire then you may want to go with 5770 (if on tight budget) because it will be fine for SC2 and if you play other games in the future you can adda second 5770. The GTX460 will not be able to have a second card added due to AMD build.