I can't seem to get the installer running for Descent 3 -- I click it, it 'runs', but it takes the better part of 30 minutes for it to actually get to the "Hey, this program is trying to make changes!" dialogue box. And after click yes to that, I still can't go anywhere.
Could this be a Windows 7 problem? I'd try it under Vista (where it actually worked fine), but my hard drive just crashed, so all I have is my windows 7 drive, bleh.

I've not used windows 7 but, can you not launch the installer in compatibility mode?

Try right-clicking the installer and running as an admin. This will give you the UAC prompt straight away and may help speed things up.

Disable UAC and try again.