Printing Errors or Lights & Stuck Print Jobs

I'm seeing extremely slow print speeds when printing wirelessly from a Mac or a Windows XP system to a new HP Photosmart Premium C309g-m printer. The printer begins printing immediately when I request a print, but it only prints one line. It will then take about 15 minutes to print the rest of the page, printing each line after a very long pause. Demo page printing doesn't exhibit this problem, only documents from programs like Word 2008, Safari and Firefox (tried firefox on PC and Mac) are affected.

If I connect to the printer through a USB connection it prints fine, so this problem appears to be with wireless printing only.

Printer: HP Photosmart Premium C309g-m
Computer: Mac mini (Late 2009 model) (also tried a Windows XP laptop as a comparison, using latest drivers from HP's website)
OS: Mac OS X 10.6.2 with all available updates installed
Computer connection method: Wired Ethernet connection to wireless router
Printer drivers: version 2.2.1 (Apple supplied, HP drivers never installed as system shipped with 10.6)
Wireless router: Apple TimeCapsule (Early 2009) 1TB, running in a/n and b/g modes on 2.4 and 5GHz. TimeCapsule is in bridging mode as the DSL modem handles DHCP service
Encryption: WPA2 Personal, no MAC filtering or hiding of the SSID.

IP addressing scheme: All addresses are handed out by DHCP server with no reservations of any kind

The TimeCapsule is sitting three inches from the printer and the printer indicates full signal. Connection of the printer to the wireless network and setup of the printer on the Mac went without a hitch. Only when printing a test document did we discover the problem. The wireless network is behaving as expected when accessing the Internet from both Mac and Windows devices (tested with a Dell laptop running XP and a MacBook running OS X 10.6.2), so I don't see any overall problems with the wireless network.

Attempted remedies:
1. Rebooting and powering off, waiting, powering on computer
2. Resetting the print subsystem, turning the printer off and on again and reinstalling the printer

3. Unplugging power from the printer and letting it sit for several minutes before trying to print wirelessly.

None of these worked.