Testing the registration of one of our plugins (DLLs) under Vista fails when regsvr32 is launched returning error code 0x80070005. This is an "Access Denied" error and has to do with the fact that under Vista, if you run regsvr32 from a command prompt, the command prompt must be started in Admin Mode (elevated).
Not only would executing a shell command to launch regsvr32 fail, but updating ther registery also gets a AccessDenied error. I ended up just turning off UAC while I tested. I suppose since our setup program accessed permission, once given, everything else worked.