Accessing shared folders over a VPN.

Hi, I'm currently running a home LAN at home (with a linksys wrt54gl router with dd-wrt) with 1 Vista PC and a laptop running XP. I can open the shared folders on my PC from my laptop and vice-versa. I recently set up a VPN(with my router, setting it as the PPTP server) and I can connect to my home LAN from school, I can browse the web through my home LAN and I can ping my Vista PC but I can no longer open the shared files on the Vista PC. If I try to open the shortcuts to the shared folders in My Network Connections from my laptop(same one I use at home) I get an error message saying I don't have permissions. My shared folders in the Vista PC have permissions given to "All Users" which is how I managed to get the shared folders visible from my XP laptop. Do I need to add another permission rule for the shared folder on the Vista PC? Might this have something to do with the internal LAN IP of my laptop? Thanks a lot in advance.