I have a Deskjet 5850. which is a networked 5550. It isn't supported under snow leopard either. I set it up as a B&W printer using the "Generic PCL Driver" and to print color I used Gutenprint. Works fine.
If you don't find the 5550 listed you can use a HP printer which is close as HP uses PCL for its printers. Experiment, and delete the printer ques that don't work.