You need to use the same username and password on all of the client PC's. In addition you should create a user with that username AND paswword on your WHS (and assign rights to the folders this user should have be able to access).
Please note that sometimes the displayed username on the client may differ from the actual logon name. Pleas check out this FAQ for more details. Also please read the Technical Brief
User Accounts and Shared Folders. This an more helpful stuff can be found
overhere