Networking password problem

Hi All,

Got a problem, I got 2 computers (main and kids computer) both running win xp pro through a router. both have the C drive shared. when i try and look at the C drive of the kids computer from the main computer I am prompted for a password even though I never put one AT ALL on either computer, needless to say I don't know what the password might be, any ideas on what the password might be and how I could disable this feature?

BTW when I can access the files on my main computer from the kids computer without being asked for a password