How can I install the printer driver for my Canon Pixma iP4200 printer?

You should be able to install the v10.51 driver for 10.7 on the 10.8 Mac. The driver is not signed so Gatekeeper will block the installation. To get past Gatekeeper, Control-click on the driver installer and select Open from the pop-up menu that appears. You will now get the option to install the driver.

If you don't have any luck with the v10.51 driver then you can install the Gutenprint driver suite, which supports your iP4200.