Make sure that you have a Windows password set for the main machine you are trying to access.
from the command prompt type:
\\computer name\c$ (c$ is the drive you wish to access, d$ for d drive, etc)
That should prompt you to login and enter a password and you should be kosher. Do this with each computer. If you want all machines to be able to talk in each direction, do this for each computer.
If none of this makes sense, MS should have a good tutorial on ther site. Good Luck!