Permissions?? where??

OK.. I have three PCs running XP going through my new SMC router/switch.

All the PCs can see each other and access the internet (works very well)..

My main PC (with the printer) wont let anyone access files or printers as it asks the other machines for username & passwords.

I have NOT set any permissions or passwords other than the standards when you

Ive turned the firewall off to no avail.

I know its something simple.. can anyone point me in the right direction?

Thanks!