Well, if the new motherboard has an additional IDE controller (like a Promise RAID), it doesn't get recognized by install unless you load the drivers. You can put the old drive on the main Primary IDE and it should come up OK. You may have to reboot a bunch as Windows removes the old MOBO drivers and discoovers and loads the new MOBO drivers. I've switched motherboards a couple times (Tyan/Via to I815 was the last one) with WIN98, ME, and WIN2K...other than the sh*tload of reboots, everything went fine, and they're still working fine.
Good Luck
Scott