Trying to setup password protected sharing

Hello,

I am trying to setup a password protected file sharing network for our small office. We have a couple machines running Vista home basic 32 bit, a couple running XP home, and one running XP pro. We have been file sharing without password protection for awhile but we are worried about waking up to a nasty prank, or worse. Most of the posts I've come across are people trying to figure out how to turn off password protection, but we actually want it on. To start, I am just trying to protect the files on a vista home basic 32 bit computer. Once I get that to work, I will move on to the other computers. I turned on password protected sharing. I setup user accounts on all the computers with the same user name and password as an account on the protected computer. Nevertheless, I get prompted for the username and password when I try to access the shared folder. I type in the username and password and the prompt screen just refreshes itself, this time with the network address and username in the username field. I can't figure out why. I read somewhere that it will only prompt you for this info if you are logged in under a username that isn't on the machine you are trying to access, or if the correctly named user account has a different password.
In that instance, you enter the correct info and get access. Well, I do have the correct username and password and it prompts me anyhow. Then, it still doesnt grant access when I put in the correct info. So, I am stuck.

Thank you in advance for any help you can offer.

Alex