Click the "Windows Update" button in the "Add Printer" dialog. This will download (amongst many others) a Laserjet 5L driver.
Not sure if these links will do you any good but they are for the Software support pages for your printer.
It appears that the current release is from September 21st, 2009 and is in the form of a CD-Rom order.
But as for drivers, Windows update will have the most current driver for your printer.