I thiks that this problem can be coused by
few routers
firewall ruls
same computer name
can you ping other computers from different network that you cannot se?
1) I can recomment try to disable "QoS Packet Scheduler".
2) And check that "File and Printer Sharing" is enabled and is installed.
3) Check in hardware configuration and chose to show all hinden devices.
4) run "sfc /scannow"
5) Check computer that sharing printer that firewall is configured correct.
if you still cannot get to other computers or print server. you can try to map it as driver letter through command line with "net use".
t.ex.:
net use x: \\server1\folder_or_printer
or use printer guide to map printer from server, look in control panel for "printer and fax" then click on "Add printer" and then click on "Network printer". You will se example there.
----EDIT----
if it is few networks and you have one printserver, then you can try to put in it few network cards and connect then to other routers.
check also router/switch if it is some rulls for ip-connection/filesharing is enabled/exist
or simple try with other (chip) router if it is possible.
WindowsXP has also build in firewall that enables if other software firewall is disabled.
try failsafe mode with network support