Make sure both are on the same Workgroup name and can see each other in Network Neighborhood. On the PC, open up the printer control pannel, right-click on the printer you want to share, and click on Share. You will need to give it a name, enable all users to connect and print to it.
On the Windows 7 computers, go online and download the drivers for your printer model, if you have a printer that offers you "Full software" and "driver only" downloads, download the driver only one.
Go to the printer control pannel, select Add printer. You will need to select "connect to a network printer", then either browse the network and have it find your shared printer or type it in manually using the \\computername\pritnername format. It will ask you for the drivers, use the drivers you downloaded.