Once you install the printer, you right-click on it just like any other sharable winXP resource, click the sharing menu option, and then click the radio button for share this printer.
As for the workgroup not being accessable, once you have all of the computers on the same workgroup (and rebooted after changing the settings), you might have to let them just sit for 15-20 minutes. That's because windows computers on a workgroup can take that long to figure out who is who and which computer is going to be responsible for distributing names.
If you still can't "see" the other computers from the my network places window, you have two things you can try. Open up a browser window (windows explorer or internet explorer, it doesn't matter) and type on of the following:
(computername is the name of the computer that has the printer)
(computername's ip address is the ip address of the computer with the printer)
file://computername
or
file://computername's ip address
Also, in case you haven't done this already, all of the computers in the workgroup need to be on the same subnet. So your router is usually something like 192.168.0.1, and your other computers might be 192.168.0.100, 192.168.0.101, etc. If they're not on the same subnet, they probably won't be able to see each other.