I wouldn't expect it to be accessed via HTTP or IPP but as just standard IP.
It should be as simple as using System Prefs to setup the printer.
Go to System Preferences/Printers and Fax and click on the "+" icon.
Click on the "IP" icon and you will see the protocol dropdown, ensure this is set to "Line Printer Daemon - LPD" (HP Printers use the JetDirect option).
Now simply enter the IP Address of your printer (in your case it should be 192.168.1.1) and the printer details should show up.
Click "Add" and you should be all done.
IPP is for printing to a printer over the Internet but as you are on a local network you only need IP printing which is just a standard network printing system.
If only everyone used Airport Extremes or Expresses because with Bonjour you don't have to do anything. I love Bonjour, she's such a sexy French lass.
