My guess is that it is probably related to the same thing that uniquely identifies a machine. When you set up a ghost, you have to remove the tag that you're talking about.
From what I've read, its the Machine ID that is assigned when you install windows. This ID is of a more permanent nature than an IP address.
Hope this helps.
A+ Core Hardware, Software Certified (May 13 2005)
the new beast...
AMD Athlon XP 3200+ Barton running at 2.16 Ghz.
GeForce MX 4000 (mainly takes the load off the main system)
Creative Labs Audigy 24-bit sound.
Some Case from tigerdirect
512 MB Ultra DDR RAM.
80GB Seagate HDD
LiteOn CD-RW / DVD ROM drive.
currently looking at a litescribe drive at staples, due to its ability to label the CD shortly after being burned.