xp network password issues

I have 3 comp's on a home network
1 is xp media center
2 is vista home premium
3 is xp pro
all three are set up for file and print share, I can see all three from any
one
none have user accounts set up
none have a password set up
I can push files from 1 to 2 and 3 with no password
I can swap files between 2 and 3 with no password
If I try to access files on 1 from 2 or 3 then a password login
window/prompt appears
since I have no password setup I am unable to access this comp.
any ideas or a fix is appreciated

Thanks