I'm posting because I hope this might save somebody else some time.
Problem - a bunch of USB printers don't work out of the box with the Airport Express base station.
In my case it was an HP PSC 1200. I just bought an Airport Express and thought this thing would be plug and play particularly since I had it printing via Linux CUPS shared via Avahi (bonjour)
Anyway - it was recognized immediately but it wouldn't auto select the driver and the list of manual driver choices didn't include a driver.
The built-in Leopard driver supports direct USB printing. I'm guessing my previous setup was using the Linux CUPS driver but I don't know for sure because so much Mac stuff Just Works :-)
Anyway - the easy fix for HP printers is to run the open source HPIJS driver. See this page
Install ghostscript, then foomatic-rip, and then the HPIJS driver package in that order.
Once that is done, make sure you close out and restart System Preferences and then when you go back into System Preferences the driver should auto detect.