just to let you know that if Skype on your Windows XP Pro machine is able to start before all the services (more specificlly Apache) are started then it is possible that it will block ports 80 and 443.
This will cause your Apache startup to fail with an error message comparable to this one:
make_sock: could not bind to adress 0.0.0.0:80
make_sock: could not bind to adress 0.0.0.0:443
Just open Skype, go to File -> Options , click on the Connection tab and de-select the 'Use port 80 as an alternative for incoming connections' checkbox.
Stop Skype and try to restart Apache.
Hope this can save someone some time ....