Hi,
Here can be many possibilities. I need more details.
-you have a domain network or a pear to pear network?
-your user accounts are local or domain accounts?
-you access this share with a domain account and also with local account?
-the useraccount which is used at XP workstation is a domain account?
-the XP workstation is part of domain (is authenticated in domain)?
Generaly if you use only domain accounts in permissions settings (also for shares) this issue don't occure.
Check permissions for this share if are based on domain accounts.
On Win9x computers don't make shares with password. Make shares and assign permission using domain accounts.