printer sharing across a mixed xp/win7 or xp/vista network is totally non-intuitive, you have to set the printer up as a LOCAL printer, not a networked one
So, assuming you have the software already installed on both machines, and that the printer is attached to the Win7 system then
1) Go into the printers and devices applet, and "add printer"
2) select LOCAL printer
3)select "create a new port"
4) select standard tcp/ip port
5) give the port a name - this needs to be the IP address of the computer with the printer. Its best if the network has fixed IP addresses, not DHCP
7) select "standard network card" as the interface type
8) now you should be able to select the correct printer through the usual setup routines and install the drivers
you may end up with two versions of the printer installed - one local, and one network. Delete the local one, or at least set the network one as the default