I am sorry to say it, but this is a problem that has evolved beyond an ATI/Intel problem or even one that involves MESA at all.  i am running an NVidia Geforce 6600 LE with current drivers and while I don't have the problems with missing torso or bad armor graphics, I do have that problem with looking around corners.  In fact, most of the doors on the outer perimeter of both towns aren't there.  I just get a strange looking hole or sometimes you can see through it clearly, but it just looks like the land drops off into blue nothing a few paces out.  I can't actually walk through, thank god.  With that being said, I have been running it on windows instead with no problems on the same computer, so it's not that big of a problem for me, but I figured you would want to know about a similar problem on a graphics card with absolutely no similarities.