depends if you activated it or not.
i installed vista ultimate oem on a new laptop 160gb hdd to test it out, decided i would wait for a while and left it at that. my then current 100gb hdd was running out of space so i thought it be a good idea to ghost the vista drive to my server then ghost the 100gb drive onto the 160gb and continue using XP on a bigger hdd, no problem there.
later on, decided that i should get vista onto the 100gb for when notebook hardware control is vista compatible, so ghosted it back so i could swap hdds when needed and on first boot was prompting me for reactivation (ffs!)
long story short: apparently as well as motherboard, it makes note of the disk id and if that changes, reactivation regardless of if everything else is the same.
not sure what would happen if i ghosted the image back to the 160gb. as i have my XP image + data on there, im not going to try until NHC works with vista.