Question : Problem: Able to authenticate to Win 2K3 using PPTP but not able to see the network

I just set up PPTP based VPN access to my recently re-designed 2K3 network.  I can authenticate to the domain and can ping domain computers but I can not access them.  I've tried both computer names and IP addresses in My Computer / IE to no avail.  When I use IE / IP addresses, I get a message that I do not have permission to use that network resource.
The problem is compounded by the fact that the VPN connection disconnects after 45 sec to 1 min, which doesn't give me much time to fiddle.
I have been able to run ipconfig while VPN is connected and verify that the client is served an address from the network, is given the proper DNS settings, and I don't see any IP addressing conflicts.
I'm using a DUN connection via Bluetooth to my cell phone for initial internet access for the Win XP client.  I think this might be part of the problem (it's very slow and there are a lot of protocols to deal with)...?  When my VPN connection drops, I am not also losing DUN.
In the past, the server was configured for L2TP and had IAS (with I/O filters enabled) / CA / IIS running.  I have turned off all those services, but is it possible they've left some residual effects that are in my way?
The network is essentially one Win 2K3 server with one NIC behind a DSL Router / firewall.  Firewall is configured for NAT and has PPTP (Port 1723) and GRE passed through to the server IP.
Thanks for any help.

Answer : Problem: Able to authenticate to Win 2K3 using PPTP but not able to see the network

Based on the type of connection you have, via Bluetooth/cell phone there may be to long a propagation delay to support a VPN. First thing I would check is the response time from a basic ping to the VPN server. If it is 125ms or less you should be OK. If not I think you will have to look to another means of connecting. One option would be remote desktop without the VPN, but rather simply by forwarding port 3389. Not quite as secure but not bad. Or find a way of connecting with better performance.