I've struggled with this problem on one of my WINXP Home boxes for years, and have simply resigned myself to jumping directly to the \\machinename\share rather than being able to conveniently browsing it from \\machinename. Finally, tonight, I figured it out (with the help of http://www.pcreview.co.uk/forums/workgroup-issue-can-see-shares-but-can-t-browse-computer-t1902202.html):
start | Run | type 'Regedit' in the box.
On the left hand pane, navigate to:
In the LSA folder, look in the right-hand pane.
look for the value 'RestrictAnonymous'.
It needs to be zero.
If it is not, double-click it and set it to zero.
( The value of RestrictAnonymousSam can be left at 1. )
Close regedit, and re-boot the server machine.