I had a similar problem. I use webmin to manage my samba server, and to fix this I had to do two things. First I had to turn all users that are on the linux box to samaba users and then I enabled guest access with r/w access. I changed the entire contents of the samba share to be user:group -> nobody:nogroup as that was what the guest user was. On my wives box I get asked for the password one time cant remeber if i did guest or nobody but it hasnt asked again since.