Make sure you have created an account on the xp box with the same username and password as you use to log in to the 2000 machine. Make sure that user has permissions to the network share you created on the xp box. Or the easy way, you can enable the guest account on the xp box and give the guest users access to the shares you create on the xp machine then anyone who logs on to the 2000 machine should have access to it.
Unsolved 
