Low FPS in TES IV: Oblivion

I get really low FPS in Oblivion. But first I want to start saying is this because I i didnt actually "buy" the game?

Here are my specs

AMD Phenom 9500 @2.20 GHz
XFX Radeon HD 6850
7GB RAM
Win7 Ult
Thermaltake 500W PSU

Thanks for any answers

Please buy it and maybe somone on here will actually help.

id also like to point out that you need to turn multi-sampling off. its a bugged setting and really eats fps (i mean serious eating my phenom II x4 and 5830 squeal when i put it over its default)