|I do not use passwords on my PCs|
So you're trying to do this anonymously?
I've had problems with XP boxes doing this recently too...
-Control Panel / Administrative Tools / Local Security Policy
-under Local Policies, find: "Network access: Let everyone permissions apply to anonymous users"
-make sure it's ENABLED. Also find 'Accounts: Guest account status' & enable if it's disabled.
Then, on your shared folders, you need to add READ (or r/w) permission for 'Everybody', under both 'Sharing / Permissions' AND the Security tab.
Eh, has fixed it the few times I've seen it. I swear SAMBA reverse-engineered this whole thing with no help, and still managed to do a better job at implementing SMB sharing than microsoft could ever do.