I'm not sure it's a vista problem because I have Vista Home premium and I didn't have any issues like that running 8.5. I have an nVidia graphics card though.

There's an 8.5 service pack 1 on www.autodesk.com website that you can download and install, maybe that will fix your problem. You will need to uninstall your version of 8.5 (but not the documentation) because sp1 is the full version. It's just the full versions with the patches built into it.