file/printer sharing - not working

I had file and printer sharing set up between two PCs and
it worked fine. One was XP Home and the other was 98SE,
and we had no problems whatever. Then we upgraded the 98SE
to XP Pro and it hasn't worked since. Other information to
date:

Workgroup name is the exactly same on both PCs
no Zone Alarm
both PCs have short names with no spaces or funny stuff
can share Internet access fine
both machines are using TCP/IP
Internet Connection firewall is disabled on both machines
guest account is enabled on both machines
XP pro machine is set for simple file sharing
no passwords on any of the accounts on either machine
XP Home can 'see' XP Pro, but can't access it
XP Pro can't see anything
If we click on view workgroup computers nothing happens for
about 30-45 seconds and then a window pops up with these
messages (both machines do this): 'xxx' is not accessible.
You may not have permission to use this network resource.
Contact administrator... List of servers is not currently
available'

Somebody pleeeeease help us with this. I see where plenty
of other people out there have this problem, and we tried
the advice they were given, but nothing works. Our
frustration level rises daily...help