For the price a 6600GT will do you fine, possibly for the whole year until you get your super computer, I have a 6600GT, and it is great for running most visually impressive games at medium settings aka Farcry. I saw the req's for oblivion, and you may need to run it at a slightly lower setting than medium, but other than that, the 6600GT is a very
good card for the money.
btw, thanks for the heads up on the PS thing, its been driving me nuts lately.
Also, have a little peep at this site to compare the cards that you are thinking of purchasing, it has good details on lots of cards -
current page = 6600 GT AGP vs 6800 GS AGP . take a look :