I am getting the same "allocate memory" error on boot. But I see slightly different issues. First off, its a Dell Optiplex GX110 tower.

X loads, but it seems unstable. One way to lock up the entire system is as follows: Load control center, go into themes and then wallpaper. When I select the dragdown for the file to use... FREEZE....

Could you post how you addressed this problem in a bit more detail? My X config tweaking is REALLY rusty.