Anonymous File Sharing from Windows 7 Server to XP Clients Without Login

I'm trying to provide machines on a small LAN with read-only, anonymous access to files shared from a Windows 7 workstation (let's call it WIN7SVR). In particular, I don't want clients to have to deal with a login window when they navigate to, e.g., \\WIN7SVR in Windows Explorer, but we do not have a domain and synchronizing accounts between the server and clients would be intractable. There are both Windows 7 and Windows XP clients that need access to these shares.

I got this working for Windows 7 clients by just enabling the Guest account on WIN7SVR and setting appropriate share permissions. Other Windows 7 machines automatically try logging in as Guest, it seems, so their users don't have to deal with the login window. The problem is with the XP clients–they can access the server if the user enters "Guest" in the login window, but I don't want users to have to do that. So from what I gather, in my limited understanding of Windows file sharing, this boils down to granting null sessions access to file shares on WIN7SVR.

But I've had no success so far on that front. I've tried all the following in the local group policy editor on the Windows 7 server:

• Set Network access: Let Everyone permissions apply to anonymous users to Enabled
• Set Network access: Restrict anonymous access to Named Pipes and Shares to Disabled
• Added the names of corresponding shares to Network access: Shares that can be accessed anonymously
• Added "ANONYMOUS LOGON" to Access this computer from the network under User Rights Assignment

Any advice would be highly appreciated… I'm mostly a Unix guy, so I feel somewhat out of my league with Windows file sharing. I do understand that any sort of anonymous access to file shares isn't generally ideal from a security standpoint, but it's the most practical solution for us in this case, and access to our network is well enough controlled that share-level security isn't a concern.