Is it an Airport Extreme base station?
And what kind of printer?
To share your printer as described, simply enable printer sharing in System Preferences > Sharing > Services or in Print & Fax. Then make sure that Printer Sharing is allowed through your firewall, or that the firewall is disabled.
Then just select the shared printer in Printer Setup Utility/Print Center on the other computer. If you're on 10.2, there's a preference item in Print Center to Show Shared Printers (I think), which needs to be checked.