Local network and annoying message

Hello! I have problem with my network, exactly with a file sharing.

I have 3 PC's in my home network. These PC's see themselves and all will be good except for one annoying thing.

If someone tries to explore shared files on another PC, he is asked to provide username and password .

I've tried to provide "Administrator" and password for Administrator of remote computer, and this works, now I can explore files, but this is problematic.

What should I do to fix this issue? I want to share files without any security.

Greetings!

First PC has Vista, second has XP Pro SP2, third has XP Pro SP3.

 

In addition to TimW's advice, have a look at this article.
Pay particular attention to the Password Protected Sharing section.
Hope this helps.