You need them in the same workgroup:
Control Panel->System->Computer Name Tab
Set the workgroups to be the same. Disable Windows Firewall on both computers and/or any other firewall, temporarily.
Now on the machine with the printer, look at properties, and share the printer with an appropriate name.
Reboot the two machines, go to My Computer->My Network Places->View Workgroup Computers.
You should be able to see each machine from the other.
You may find that you now have an 'Auto' printer popped up in your network places, otherwise, go to Printers->add Printer->Add a Network Printer->Browse for a printer.
Browse your way through the workgroup and you should be able to add the printer.
Now re-establish the firewalls and see if it still works, if it doesn't, you need to start playing around.
The above represents the perfect situation where nothing goes wrong.
BW