XP IPSec VPN Networking

I have configured a Draytek router to accept connections from
teleworkers. The teleworkers are most of the time in the office and
physically connect to the 2003 domain. When they try and connect from
outside the office, there are problems. The VPN is true, I can ping
the fileserver, I cannot browse any folders on the server, nor can I
get Outlook2003 to connect to the Exchange2003 server. I am
continuously prompted for a password. The error messages are varied,
sometimes relating to DNS settings, sometimes relating to the PC not
being allowed to have multiple connections to a server.

I have a notebook that has never been joined to the domain. This
connects perfectly every time. I am prompted for a password once and
it lets me browse the domain, file structure, email etc.

I am sure the VPN config is okay, I suspect there is a domain policy
or something that I need to change to allow the domain teleworker to
connect. Can anyone shed any light on the issue?

Thanks in advance.