how to autehticate clinets - router to router vpn ?

Hi,

- I have an NT4 server at site A and various windows clinets at site B.
- I have used routers to connect each site using vpn, the conneciton exists
24/7.
- I wish to map a drive from the clients at B to the server A.

1. What is the best way to authenticate the remote clients on the remote NT4
domain to allow them to access the share / mapped drive ?

i.e
- should i just allow EVERYONE access to the share and therefore i should
not be prompted for user + pass ?

2. In order to map a drive over this network, how can the clinets find the
network share after the router to router vpn link is established ?

i.e
- enter a static router in the router pointing to remote subnet ?

Thanks
Scott.