local & domain path query

hi I am running a win 2003 domain and getting ready to migrate across to win 2008.

I have noticed something unusual and wanted to know if anyone can provide any advice.

step 1

usually I install win 2003 on the physical server and join as a member server to the domain.  when I then open up the cmd prompt it shows the following path:

c:\documents and settings\administrator.domainname>

if I logon to this same member server (locally) and open the cmd prompt it shows the following as expected:

c:\documents and settings\administrator>

step 2

I have installed from a win 2003 cd the image onto my ris member server.

I then logged onto my (aduc) and pre-staged my isa 2006 firewall by adding the name: isa-20061a & the mac address successfully.

I then rebooted my other server and selected (f12) and installed win 2003 image successfully.

on completion of install I logged on as the domain administrator as it does not currently have a (local account) like (step 1) above as expected.  I then opened up the cmd prompt:

c:\documents and settings\administrator>

I then created a new (local account) and opened up the command prompt and saw:

c:\documents and settings\administrator.isa-20061a>

question 1.  why is (step 1 different from step 2)  ?