Firewall is definitely your best protection (ZoneAlarm is OK for a personal system). Of course nothing is fool-proof completely but firewall is the best case. To change your port:

1. Go to Ontrol Panel
2. Select Administrative Tools
3. Select Internet Services Manager
4. Right-click on the web-site and select properties
5. Change TCP port to a different port.

To access your site afetr you make this change you will have to add a :number to your URL address (where number is the new port number you have selected).