If you are getting the error
"The port specified has already been chosen. Please choose a different port."
when trying to configure the Central admin then you may find that the issue comes from your machine name.
Building a Demo SharePoint Environment I was encountering the issue. I was stumped with the above error and no matter what port I tried I could not get it to work.
I foudn the problem when working through the logs.
06/26/2008 16:07:21 1 INF Searching for a duplicate site http://MOSSDEMO#2:11000/
06/26/2008 16:07:21 1 ERR Found a duplicate site http://mossdemo:80/#2:11000/
It looks like the # is used as a delimiter and throwing the everything out. I renamed the machine and all sweet.