On my local development environment I run both IIS or Apache depending on weather I'm doing ColdFusion or PHP development. I run both of those servers on port 80 and use manual scripts to start them. I recently installed Skype on my development box and afterwards none of my local servers were starting properly!
I ran a netstat - ab and found that Skype was listening on port 80! Looking at the Tools -> Options -> Advanced -> Connection setting in Skype I found a little checkbox that says: "Use port 80 and 443 as alternatives for incoming connections." I unchecked this box and my webservers started again!