Don't know what's happening with your VPN. I CAN tell you that I just tried my PPTP VPN (hosted on SBS 2003) from my Vista Ultimate test box and that one's working fine. It connected right up and I can browse shared folders.
What kind of VPN Server are you using?
Are you using the built-in Vista VPN client, or a 3rd-party client?
PPTP, L2TP, or ?
Is it possible that since Vista has network browse disabled by default (so that we are protected from ourselves) that it is preventing you from seeing your resources? If so, do a windows help search to enable it.
Sorry...They call it "Network Discovery". I thought I used the word browse as the term in the Windows help search to get my first Vista system to see the other computers and the shared folders in the workgroup.
I had a similar problem when using VPN to connect to my servers, Network Discovery is located under the Network and Sharing Center (typing Network Discovery into the Start Search doesn't pull up anything). Also under Remote Desktop Connection make sure that if you are using TSG to connect through a firewall, that you have configured that as well.
A TSG is a terminal service gateway, it is commonly used by businesses as the gateway connection for remote users without having to setup VPN. If your gateway is using port 443, the chances are you are using TSG and will need to enable it under Advanced > Settings.