Sadly, I can't confirm any of this, but Cedega claims to have Oblivion working by using the Oldblivion drivers (details at http://cedegawiki.sweetleafstudios.com/wiki/The_Elder_Scrolls_IV_-_Oblivion). The main issue, apparently, is that current generations of Wine do not (yet) support the advanced video rendering modes required by the stock Oblivion installation; Oldblivion (found at http://www.oldblivion.com/) addresses this by providing software-level emulation of these required features, thus allowing Oblivion to function--albeit at a reduced pace--with older video cards.
Unfortunately, I can't confirm any of this, as I do not personally own the PC edition, but maybe somebody who has it can confirm?