Ulmont, what kind of Windows Vista are you running? I run Home Premium with 2GB of RAM and Unreal Editor works fine.
Well, I have an XP, and it runs fine on that. On this comp (the one with unrealed issues) I'm running a custom-built Windows Vista Ultimate 32 bit with 3.5 gigs of ram and a 3 ghz processor. It's probably my graphics card (It's a NVIDIA geforce 9800x or something like that).