Well, I just recently bought DiRT 2 during one of those damn Steam sales, and now I'm finally getting to play it.  However, I'm having issues with my graphical settings.  While a few settings I can set to Ultra, the majority are stuck on high, with post-processing on medium. I WANT THIS GAME TO LOOK SEXY.   
 
I can't use DX11 right now, due to the fact my gfx card is a GTX 280, but there is no reason I shouldn't be able to turn textures and other stuff to ultra.  The DX11 should only affect the tesselation and ambient occlusion settings, AFAIK.  My  understanding is that the game locks the settings due to memory, gfx card memory, and cpu speed, much like GTA IV.  With my rig, however, which is fucking beasting on the settings I have it on now, it shouldn't be a problem in the least. 
 
GTX 280  
AMD Phenom X6 1090T Six Core Processor 
4 Gigs RAM 
Vista 32 Bit. 
 
Please help!

I don't know, really. I've maxed that game out no problem, even with a lesser rig. Perhaps there is some possibility to change the settings pre-launch. You know, the typical video settings screen which appears on some games when clicking the icon to launch it.

First off, there isn't even a texture setting in Dirt 2.  There are 4 settings on 'high' that can't be turned to 'ultra' and the post processing medium as you say.  Are you sure those 'high' settings even have an ultra in DX11?  Even if they do have ultra levels it may be DX11-only effects.  It's all stuff like 'lighting' and 'particles'.  I don't think you're gonna be able to enable those either way.  If you take a look at comparison screenshots there really isn't much difference anyways.

What Diamond said. There are some settings that max out at high regardless of DX version, so high's as far as they go.

Yeah, some settings are locked to high. The game looks fucking amazing maxed out will all settings in DX11 @ 1920x1080 60hz vsync. 
 
I have all versions of the game, pc version with my 5870 is just unreal.