Hi-
Reseal is a function in the WinXP OEM preinstall kit... I suspect you know that or else you wouldn't be asking. Anyway, the idea is that the OEM uses the preinstall functions to install whatever software, updates, branding, etc. they want on the system. Once that's done, the install can be resealed & the computer delievered. All that happens then is that the end user has to go through the activation steps again and agree to the EULAs. Then once they boot to the desktop, they'll see whatever you left for them, be it branding opportunities, software patches, links, or whatever. Just don't overdo it!
-Chuck