Windowsasking for user-name & password to access shared network drive

Hello, i have 4 pc in my LAN with all 4 accessing internet. it is a peer to peer environment all under workgroup "mshome"

i have shared some drives in all 4 of them. with full access to "everyone" so ACL n security is not all a problem here.

3 of them run on XP and one on windows 7.

2 of the PC's can access the shared network PC (and hence the shared drives) easily without being asked for user-name and password.

But here 2 machine keeps asking for user-name and password when trying to access other network pc's (forget shared drive, it ask for authentication while clicking on the pc name shown in my work-group)

None of the pc's have any sort of user-name and password. there is no such thing as password not even to the Administrative account which gets created by default.

I am puzzled why it keeps asking for user-name and password when trying to access other pc's,

all are pinging each other just fine. no issues of firewall of windows or of any AV.

please if anyone can help....thank you.