file sharing between laptop and computer

I am using win 7 on desktop and win Vista on laptop. I installed Netgear wireless router to my desktop. The internet is working fine on both the systems. But there is a problem in sharing the files. I have selected the "Public" folder to be shared. But when I click on the other systems icon in the network column of the control panel to access the other systems shared files on the first computer, it is asking for username and password, although I have not set one. I have tried all sorts of passwords which I may have accidentally set but to no use. This problem is both ways.

So what should be the username and password for this by default or at what stage may I have set it, if ever I set it myself?

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