What are your PC specs? The below figures are approximations based on a mid range system.
An ATi HD 4670 ($65) can run Oblivion at 1680 x 1050 with 4xAA and 16xAF at 30 fps.
An ATi HD 4830 ($99) can run Oblivion at 1680 x 1050 with 4xAA and 16xAF at 40 fps.
An ATi HD 4850 ($140) can run Oblivion at 1680 x 1050 with 4xAA and 16xAF at 65 fps.
The rEVOLution is not being televised