vista problem

hope somebody can help as this has me stumped. Setup a new pc for a friend who has a file server(not on a domain) and 3 xp pro machines in his office. He bought a new pc with vista basic on and i got it setup for him.Mapped a drive to the server to access files and worked ok. rebooted and got the message cant reconnect to mapped drives. if i click on the mapped drive a pop up appears asking for the password for the server. enter this and access granted but reboot and same problem. i created a user account on the server and mapped a new drive and entered new user details at prompt for user and pw. reboot and same problem again. im sure its something simple that im missing any help much appreciated.