Heh. I registered just to post this reply.
Anyway, I have the same printer. It's a damn fine one too.
As you said, it's recognised imediately in Jaguar. However, if you open the Print center application and highlight your printer, you can do apple key + I (or choose info from the menu).
This should open a secondary window, with info (well duh

) on your printer, and a drop-down menu.
When you choose ppd (which iirc stands for postscript printer definition file), the second option from the drop down menu, you should notice that it uses a generic ppd file. You should change this ppd to the HP Laserjet 1200 ppd (it's is another drop-down list), click to accept changes, and you should have more printer-specific options when you go to print a file (like fastres 1200 (default), 300 dpi, 600 dpi and 1200 dpi, and the watermarking and stuff.
I hope I was clear in my instructions, and I hope this reply helped.
Cheers.