My question is do you want to spend that much money on a new graphics card for that computer. If you do, find out if your motherboard supports any of the newer graphics cards, if not I'd look into a new computer. Oblivion is a hell of a game, it really takes its toll on a computer. It's pretty much only the brand spankin new ones that can handle it on full detail and resolution.
EvoN1020v, Titan Quest was not coded very well imo. My friend has a Gen 2 XPS lappie, and I have an i9300. And at random moments the game will just crash on us. I'd look around for all the patches you can find for that game. It's buggy:-(