XP Pro VPN Server - VIsta Connects, XP wont

[DontStealMyFish]

ok let me clarify: im using xp pro as a vpn server. i have it set up behind firewall. i can technically connect using both xp and vista. however if its an XP client that connects, i cannot ping the client, nor can the client ping or access shares on the server. Now when a vista client connects, there is no problem, i can ping the client, the client can ping me and access shares. i have tried using a few xp clients, same problem everytime. curretly i have the following ports forwarded to the server:
UDP: 500
UDP: 4500
UDP: 137
UDP: 138
UDP: 1701
TCP: 139
TCP: 1723
TCP: 3389 (i know, i just have it for testing)
Protocol 47 [GRE]
Protocol 50 [ESP]
Protocol 51 [AH]

any ideas as to why i cant view shares or ping on the XP platform? thanks.