acessing shares from a vpn client

I have a winnt4 domain with an ISA server connected to the internet. I have vpn set up on the ISA box. When I connect to my network via a vpn connection, I am prompted for a username and password to access a share.
What do I need to look at to resolve this problem.
BTW, I have thought of the need to have the vpn clients workgroup set to the domain name that I’m trying to connect to. I have also, made the vpn client a domain member with no sucess.
Thanks
Jeff