How well will ob run on this system?

2.00Ghz CPU
2.00Ghz RAM (DDR2)
ATI Radeon 4300/4500 graphics

I have a Radeon 4550 and it's running rather well as long the resolution isn't too high.

You don't mention what kind of CPU it is, though, so I can't comment on that. But it should be powerful enough to run the game.

its a dual core but then again multi core doesnt make much difference...im trying to get more ram but i know that it wont be much use and i cant get a better cpu so im hoping that the graphics will make up for the loss in performance im expecting

There's a comparatively large difference between a 4350, which is essentially just junk, almost like an onboard chipset chip, and the HD 4550, which three years ago was a borderline part, sitting much higher in the business class, which is the near-bottom (IGPs, especially Intel, being the absolute bottom), and the Mainline Medium cards used for games. As old as Oblivion has gotten by now, the HD 4350 is usable, but pretty poor overall, while the HD 4550 is "practically" decent (for this game in its dotage).

If you don't know which is which, and which yours actually is, you do need to find out. I looked them up, and the VRAM specification for the better 4550 is half again faster than for the 4350.

http://www.gpureview.com/show_cards.php?card1=585&card2=584

Oblivion is closer to being CPU bound than to GPU bound, so an ordinary graphics card with nothing particularly amazing about it isn't going to make up for a slow-running CPU.

My card is the radeon hd 4350...so basically from what you're saying it's pants...

Wow, freddo I remember that name...

The card should be fine unless you are running stupidly high resolutions. I am playing the game with an HD2600 and a prescott 3.4 (all high settings, AA 4x) and it looks just as good on resolutions of 1152x864 or 1280x720. Infact, if the res is too high I dont get that pastel feeling, buildings look too....ehm...defined.

The HD 2600s were Mainline cads four years ago, and therefore not that comparable to an HD 4350. Remember, the "4" in front usually means only the age, while the "350" means bottom of the barrel, with only a 64 bit memory system.

http://www.gpureview.com/show_cards.php?card1=522&card2=585

Whatever your CPU is will make a huge difference, too. If that's a p4, good luck, but if it's an i7 it'll run anything without issue. The clock speed is pretty irrelevant.