On Leopard, replace steps 3 and 4 with:

3. Go to the Apple Menu and Choose System Preferences. Click on Print & Fax.
4. Click the + button on the left hand side near the bottom. A window should pop up. Right click on the bar at the top (next to More Printers for example) and choose ‘Customize Toolbar’. Drag the cog-shaped ‘Advanced’ icon onto the bar next to the More Printers icon. Click Done. Click the Advanced icon. You may need to wait a few seconds while it loads. For Type: choose PDF Writing. Leave Device as it is. For the URI, use pdf://pathname, where pathname is where you would like the PDF file to be saved — I set mine to PDF://~/Desktop so that it saves the file onto my desktop. Give it a descriptive name (e.g., PDF Writer). Change ‘Print Using’ to ‘Generic Postscript Printer’. Click on Add, and it is all ready to go!