would a (PCIe) Geforce 7600gt push Oblivion all the way up lighting and all or should i upgrade to 7800gt or dual 7600gt or 7800gt

wow, you're lucky to have the choice. I guess it will depend on what resolution you want to run it at, but I'm guessing since you're going this far you won't want to run it at 8x6! As far as graphics, too much is never considered bad.

I don't think it's worth going dual 7800gt as the increase you get will not be worth the money and no way near 2x performance. Dual 7600s would be what I would do if I had the choice as you'll see a greater % performance increase over a single 7600. Since you seem to have a bunch of cash avaiable you may want to consider getting a 7900 if you can find one. This way you'll keep a slot free for another 7900 further down the road. :)

i agree totally with al on this one :D

well i dont have a lot of money at the moment just saving up, but would a single 7600gt play oblivion in 1280x1024 and vid settings turned all the way up fine?

7900gtx a bit to much for me lol ($499 at tiger)