Use the control panel Beta version in your XAMPP root. Click the netstat button BEFORE you try to Start Apache. If something is running on Port 80 OR 443 it should tell you - both 80 and 443 have to be clear for 1.7.7 to run on Windows.
I have to work on a remote server update for 'work', so I may not be back for a while, some of the others may catch your answers. I'll check when I get a chance.
The World Wide Publishing service is known to take up this port on Windows 7. You can check to see if it is there by opening your services manager (Start > Run > services.msc). If it is there, you can stop and disable it.