RegSvr32.exe on Vista

Calling regsvr32.exe against a COM dll will give you a 0x80004005 error from DllRegisterServer. As it turns out, the UAC in Vista was what was causing this.

The way to get around this is to Right Click on Start All Programs Accessories Command Prompt, and click Run as administrator. Once you have the elevated command prompt, you can run the command as you normally would.