I finally found a solution for Oblivion running poorly on my PC; upgrading DirectX 9.0c to the April 2006 version. No idea how this 9.0c is different from the older 9.0c that was on my machine, but it's smoothed out the framerates significantly. Much more success than trying to various tweaks. PCs are such a mess; Oblivion definitely runs better on the Xbox 360.
  2006-04-19 15:02 Z