As I recall no XP disk will upgrade 2000 to XP in the way previous versions of windows did.
Even though they both can use NT file system the programs are completely different, so XP requires a clean install.
It's been a while, but as I remember any XP disk can upgrade, so to speak, and will ask if you want to save your files.
It will then save all your personal files and reinstall them after it formats and installs XP.
The XP disks that are called upgrade are the same as the regular version, but because they are cheaper they will ask you to put your previous version in the CD ROM just for a second or two to verify you have a previous version. As I recall any 98, ME or 2000 disk will work for the verification. That's the only difference between the two. Your corporate disk will upgrade in the new way.
A word of caution, the saving and reinstalling thing didn't always work, so back up everything first.