If you are getting server 500 errors when you are trying to browser out of IIS 5.1/7 – and nothing is adding up at all – check your event viewer. You probably have something like this in it:
Event Type: Warning
Event Source: W3SVC
Event Category: None
Event ID: 36
The server failed to load application '/LM/W3SVC/1/ROOT. The error was 'Class not registered'.
If you are getting this error, it means more than likely that your COM+ catelog is corrupt, and does not contain the registered IIS components.
Use this link to fix the problem (follow it exactly as it stands, and your problems will go away!)