First, download and install Gimp-Print on the Mac. Now open up Print Center (Applications -> Utilities -> Print Center). Hold down the "option" key while you click "Add". This gives you more options for adding printers. Select Advanced from the drop-down menu, and then select "Windows printer via SAMBA" for the device. Give it a name, and type in the path to your printer. Something like:
Where: the username/password is the login for the Windows box, winbox is the hostname of the Windows box, and printername is the name given to the shared printer on the Windows box.
To get the name of the shared printer, open up Terminal and type:
smbclient -L hostname
where hostname is the name of the Windows box. Enter the password and it should spit out a list of all the available shares, and you can locate the printer.
Additional information can be found in the Gimp-Print for OS X FAQ.
Note: Gimp-Print does not currently support the HP DeskJet 700 series printers. A work-around is possible, but it is a bit more involved than this. Instructions can be found here.