kit it simple. first on windows xp turn on file and print sharing.
http://www.bleepingcomputer.com/forums/t/43840/how-to-check-your-workgroup-in-windows-xp/
change your workgroup name from home to (yourcompayname) or (work workgroup)
something that you remember.
on the two windows 7 pc under networks set up connect to a new workgroup. put in the new workgroup name and turn on file and print sharing. then reboot the pc's
if you did it right under my computers /networks you should see the other two pc.
under the windows 7 pc click add network printer under printers. (it should find your printer).
you may have to install the printer software on both the newer pc.