In Orcas you can also install TFS on ports other than 8080. Again you will have to specify the port in MSIProperty.ini file. You still cannot use a port number that is already in use. We also don't try to merge sites for you. We do expect you to have a dedicated port for TFS.
Following are steps you can take to install TFS on non default(8080) port.
At the end of setup you should have TFS server up and running on non 8080 port. You may have to open the NewPortNumber in your firewall to make things work.