Windows Domain Login across VPN using snapgear vpn server

I have a few users that are using PPTP VPN to access an office network.  

Users network:
-Clients are all windows XP
-Clients are using CISCO/Linksys WRT320N
-Clients have NAT and DHCP enabled
-WRT320N provides dhcp address for local network
-VPN has "use default gateway on remote network" unchecked
-VPN has DNS set for Domain controler on office network
-VPN is setup with password saved and has "anyone who uses this computer"  checked


Office Network:
-SecureComputing/SG565 router
-Router had nat enabled
-Router has a PPTP server enabled

The current configuration has:
-PPTP/VPN  into office network. SnapGear provides DHCP ip address and authentication.

Desired configuration:
I have converted one machine to be a member of the windows domain in the office.   This occurred when the VPN was manually connected.  But what i've found is that when i try login to the domain, the machine will not automatically dial the VPN.

In the login dialog for XP they have a checkbox that allows you to dialup a network, but its not a VPN dialup, is an modem dialup..

These are possible solutions ive read online:  

1) In the PPTP VPN in the options tab under dialing options, enable include windows logon domain. I believe this works if the VPN server based a windows  VPN server?

2) I read that I should have "anyone who uses this computer" checked in the vpn setup.  In addition if the username/password for both my VPN connection username/password and domain username/password are the same, then XP would use that PPTN VPN connection..  I dont know how to make XP trigger this..   Put the VPN in the startup folder??

3) Others said that i should use a IPSEC VPN.  

So experts, please give me some suggestions..  I hope you can provide me a simple configuration change that will make this work with my snapgear and PPTP configuration.

If this is not a workable solution, please provide some suggestions that will not require me to swap out my  router..

Thanks