Draytek router and VPN passthru for Windows Server 2003

Hi all,

we as an organisation have been using Draytek routers to establish vpn
tunnels (lan to lan) between the office and home workers. It have come
to th point now where we need to be able to configure a Windows 2003
Server as a VPN server and have vpn passthrough on our router (a
Draytek 2800g)

I have looked at the draytek website and tried to understand how this
is done but its just not making any sense.

What I really need is for anyone who is authorised to create a vpn
network connection on their home machine, using the WAN ip address of
our router and their internal network credentials, and login to the
domain THROUGH the router, not create a remote dial in on the router.

If anyone has done this and knows what I need to do to the
router/server to get the working, please let me know.

Thanks.

Karl