Im having a lot of problems trying to run unity on windows vista business edition. Everytime I try to open any project I get the error "the process can not access the file because it is being used by another program".
you might have problems with UAC. try to run unity with admin privileges. right click on unity and choose run as administrator. also try to create projects in document folders and don't create them in windows root or ...
Yep, that's Windows Vista for you. My coworkers I have encountered this many times, in non-Unity related situations. Hopefully Windows 7 is the answer. I haven't used it.
This is sometimes caused by anti virus software running on your machine. If your AV software tries to do a real-time scan on files created by Unity it is possible that those files get locked by the AV software, preventing Unity from continuing to write them. If retrying gets things going (even if after 10 or 20 attempts) then you may have this problem. If so, consider temporarily turning off your AV software (with your machine disconnected from the network). If the problem goes away, then consider telling your AV software to not perform realtime scans on Unity project folders.