When a VPN connection is established, one of you (you need to tell us which of you you have this setup as right now) connects to the other's private network.
ie. Someone has a router and either one or a few computers (doesnt matter) all setup to use a 192.168.x.x ip address but they are also connected to the Internet and have a public IP as well (the ip address everyone else sees and has access to). Well if the other person connects to their VPN server with a VPN client, then they should too receive a PRIVATE ip of 192.168.x.x.
So the question I have is when you said you can ping his 'remote' IP, what did you mean by that? Can you ping his PUBLIC IP of (most likely 6x.x.x.x or 2x.x.x.x) or did you mean you can ping his PRIVATE IP of (most likely 192.168.1.x)?
If you can ping his PRIVATE IP, then that means that somehow you guys do indeed have a sucessful VPN connection. The next step in finding out why you can't initiate file-sharing would be to:
1) first verify that each of your OSes are correctly setup for file-sharing, best way to test this would be to connect to computers locally on your own private networks
2) make sure you arent blocking the necessary ports for windows file-sharing (not sure exactly which ports/corresponding protocols are responsible off the top of my head but to be safe make sure all of the following are allowed [135 [TCP], 137 [UDP], 138 [UDP], 139[TCP], 445 [TCP]]
3) if both of the above are all good, then the next step would be to try manually connecting to the computer by going to start->run and typing "\\[name of other person's computer]" and see what msg you get. if you are able to connect, then you should be able to go to 'My Network Places' and see his computer there, and you can then map drives to your heart's content.
lemme know what the verdict is.
~jeff~