Should be the same for both 10.3.9 and Tiger. Select the item(s) you wanted zipped and hold down the <ctrl> key, then press the mouse button while still holding <ctrl>. A menu will pop-up (called a contextual menu b/c it changes based on what is selected/pointed at when you bring it up). In that menu is a comand for <create archive of ....> and the name of the item(s) selected. selecting this will make a zip archive of your selection (does not delete the original).
Tiger (and Panther) can decompress zips natively, though, so as far as that goes, there's no real need for StuffIt. The only thing you need StuffIt for is sit and sitx (StuffIt) files. And possibly rars (I'm not sure about that).