"...they keep asking for a password." And I suppose there isn't one.
Oh Dear! Another variation on the theme of protection getting in the way of productivity. With me it's the other way around.
My XP machines want my Win98SE machine to log in (UserName but no password).
May I suggest that, on the XP machine, you go to the Users part of Control Panel and check that the Guest Account has not been disabled. Machines accessing XP on a peer- to-peer LAN are always granted Guest status and have the limited privileges that you may have given the Guest User Group.
Hope this Helps. fobs