Downloaded Bitnami Multisite Stack; can't use port 80

I recently downloaded the Bitnami Multisite Stack. I tried to complete the install but I keep getting an error saying "Port 80 is in use" and that port 80 is the only port Multisite will work on. Not sure what to do... I am using a Mac OSX if that helps. Thanks in advance. (Oh, and I saw on several other threads that Skype might be the problem, but I don't have Skype).