Windows XP giving password prompt for Network share

We have a workgroup that has 12 Windows XP pro workstations and a SBS 2003 server. The It tech before us had set the workstations up on a workgroup, and the server as a domain controller. We came in and have demoted the server to the workgroup (we can't put it on a domain at this time, hoping to do that in the future).
However, all the workstations have a mapped drive pointing to a shared folder on the server that stores the data for a program that is running on all the workstations. we can map the drive (which we set up for anonymous access), and the users can connect. However, several times a day the workstations will begin to prompt for a password and username. We have put in username and password, told it to save it, it still prompts shortly after. We can put in a bogus username and no password and it still connects just fine. We want to disable the password prompt on the workstations so that the users can just access the share without prompts. If possible.
We've enable the group policy to allow the Everyone user to access the server from the network, gave permissions to Everyone for the share, and about everything else we can think of.