We had a situation where a brand new web application needed a new host header and be moved from a high port to port 80.
Use this guide to add a host header.
Make sure you use the Default zone (or else you can not browse to 'Advanced Permissions' or add web parts).
Update "My Site" settings in the SSP
Recrawl the content source which index the user profile database, or else you will not be able to search for users.