William,
You could have drives mapped from your W2K box to SME already or you have a share open in a window somewhere (or even a printer connection).
You must remove all connections from the W2K box to the SME server first before attempting to join the domain. Open a command prompt on the W2K box and use the command :
NET USE * /DELETE
then try joining the domain. A search of the forums will bring up more details as this issue has been discussed often.
Kelvin