Sonicwall and Windows XP

I have site-to-site VPNs configured for multiple offices. connections from Win XP machines can connect to servers across the tunnel. however, Win xP machines and servers CANNOT connect to shares on other Win XP machines across the tunnel. Win XP and server machines CAN connect to other Win XP shares on the SAME SUBNET. any ideas why i cannot see a Win XP share across the VPN tunnel??