I've used Comodo on Vista and it was alright. The only real annoyance that I got was if I didn't put it in "Installation Mode" before I started an install, I ended up with a bunch of pop-ups requesting permission (even after selecting Installation Mode at some point later on). Although this wasn't on every app, it was enough to be annoying.

I haven't tried it on Windows 7 yet, so I honestly can't tell you whether it works or not. During the Technical beta (at least the early stages) they didn't have a compatible version.

Have a great day
Patrick.