Setup asking for 2 users during Installation

I haven't seen this before.

Recently, I brought out an older P4 machine (IBM Netvista 8319), and decided
to install Vista on it. Everything went well until the final reboot. Instead
of going to the desktop, I first got a screen asking if I wanted to run
Windows in Safe Mode or Windows in Normal Mode, etc. I chose Normal and up
comes the setup screen asking for a User name (again). I entered my original
User name, but got a message saying it was already in use (or something to
that effect).

So, I chose a different User name and password, and the installation
completed. I ended up with 2 administrator accounts, one in each of the
names.

I have installed Vista on a good many new computers, and never found this
problem.

Can anyone tell me why this particular setup wants me to enter a second User
name and Password? I can't see where the hardware would be doing it. There's
nothing but your standard components involved.

Thanks.

darkrats