When FrontPage starts a web-server starts automatically.<br>
Port 80 error means that FrontPage is not able to load the Web-Server. <br>
To solve the problem, re-install FrontPage. While Installing, choose the Custom Install Option. In Custom Install, be sure to tick the 'install-server' ( may not be the exact phrase ) option.<br>
Best thing would be that in the Custom-Install, you select all the options. <br>
I am sure, this will solve your problem.<br>