On your installation CD, open up the Support\Tools folder. Open
the Deploy.cab file. Right click on setupmgr.exe and select
Extract. Save it to your desktop. Run the Setup Manager program
and enter settings that are appropriate for your situation, one
of which will be your CD Product Key. Once you've created your
answer file make sure you've named it winnt.sif. You then put it
in the I386 folder on your CD. You can also put it on a floppy.
Here's a site that might help you understand the process a little
better.
http://unattended.msfn.org/xp/winnt_sif.htm
Also, you might want to consider using a rewritable CD. That way
you'll be able to change your answer file for different
situations.
Nepatsfan