I am having the same problem.
I have a laptop running Win XP Home 2002 SP 1 (i call it Shemp)
I have set the "sharing and security" for the Shared Documents folder such
that:
"Share this folder on the network" is checked as is
"Allow other users to change my files"

However, I cannot see the contents of this file from my other computer (also
running Win XP Home 2002 SP 1).

When I attempt to look at the directory I get:
"\\Shemp\SharedDocs is not accessible. You might not have permission to use
this network resource.  Contact the administrator of this server to find out
if you have access permission.  Access is denied."

I am able to share the entire C-drive on Shemp (and can see the root
directory) however I can't see the Shared Documents or the "my documents"
directory of the only user on the laptop or the program files directory.

Interestingly enough, I can see the folders in \\Shemp\C\Documents and
Settings\All Users and can open the Desktop, Favorites and Start Menu
folders but not the Shared Documents folder!

In your answer below, Roger, you said "does the account used to attempt to
access the files have a corresponding account defined on the sharing-out
machine "

I have no idea what this statement means.  Can you elaborate???

Thanks!