Is WinXP corporate the same as pro minus activation?

Yep. A few different files, but the same OS. The MSDN version may not even prompt for a serial number (as can be setup by modifying a file) either by default, let alone activation.

Can anyone give the directions for editing the correct file so WinXP setup doesn't ask for the serial number? I did this to my Win2000 slipstreamed sp2 CDrom that I made, it's one less thing to hassle with during the install. I've looked around for details on this for XP but haven't found any info and this is the first time I've even seen the topic brought up. Thanks...

winnt.sif in the i386 folder

you can make your own winnt.sif
from the 2k/xp cd, go to support folder.
extract the files from the deploy.cab
then run setupmanager.
create an unattend installation file.
it will create an unattend.txt with all the answers that you have provided.
rename the unattend.txt to winnt.sif and put it back to the i386 folder, and you will have an autoinstall CD

good stuff FatFish