Extender can't see shared folders on network

I have two machines on my LAN (other than the MCE) that contain media
that I want to view on the MCE and on the extender. One of them has
MP3s, the other has pictures and WMV videos. Both are XP pro with SP2.

Problem is, the extender "sees" one of these two machines, and it
doesn't see the other one. To try to find out what's different between
the two, I went to the MCE machine, brought up Windows Explorer, and
looked under My Network Places, and I see all three machines show up:

+- MSHome
+- MCE05 <-- the MCE box
+- PC1
+- PC2

Now, if I click on PC2 here, I see the shared contents of the machine
(Printers & Faxes, shared folders) just fine. But if I click on PC1, I
am immediately prompted for user name & password. Now, if I enter my
user name & password for PC1, it then shows my shared contents, same as
PC2.

The shared folders on PC1 all have read-only access granted to
"Everyone." The Guest account on PC1 is enabled. The XP firewall is
turned off.

I suspect that if I could fix whatever is causing PC1 to prompt for
user name & password, my extender would be able to see that machine,
but I have no idea why one prompts for it and the other doesn't. My
understanding was that if you see a machine under My Network Places,
you would be able to see all of its shared resources (printers, etc)
without having to authenticate, and only if you want to see something
like an admin share, would you have to provide authentication. This
seems to be the case on PC2 but not on PC1.

Can anyone tell me how to stop PC1 from prompting for user name &
password?

Thanks,
John

I solved it by turning on "use simple file sharing", which before was turned off
on all computers. Not sure why this fixed it but
.. . . at least it works.

John