Point 1: You should always install MOSS while logged in as the account that will ultimately be used as the service account.  This is because during the install whoever you are logged in as by default get's admin access to just about everything.

 

Point 2: If you need to later go back and create another "Super Admin" user account, there are a number of places you need to do this... here they are in case you forget (most important required ones are in red):

1) Farm Administrators - add from the operations page of central admin (security configuration)

2) (optional) Site Collection Administrators for CA - add in the site settings from central admin. 

3) Site Collection Admins for your SSP - add in the site settings area from your SSP site.

4) Shared Service Rights - Add all manage rights in the "Personalization Services Permissions" section of the SSP

5) Make sure account is in the owners group on all Applications (done in the People and Groups area of each root level web of each site collection)

6) (optional) Add user as either primary or secondary site collection administrator for all the web app site collections (don't mess with the MySites though other than the root).  Do this in "Site Collection Administrators" on the Application Management section of Central Admin.

7) (optional) Set up full control policies for the web applications.  Do this in the "Policy for Web Application" under the Application Management section of Central Admin.  Make sure you don't check the box "Treat account as System" when doing this unless that's really what you want.  This will make sure the account can access/modify anything and everything that gets created in the entire web application.

 

Hope this helps someone.