Microsoft VPN

Ok I can get VPN to connect using microsoft vpn adapter etc… on client side, connecting to NT4.0 server(PDC) via ras using PPTP. but its like it has a mind of its own….some accounts can log in some can’t. Sometime you can see network in networkneighborhood, sometimes you can’t…anyone know where there might be a complete manual on setting this up spo i can see if i am missing something?