When you say that you have "checked the 'separator page' settings," I hope
you mean that you have examined that setting and have made sure that "Use
Separator Page" it is not turned on, as opposed to having *check-**marked**
the separator page option.
I would delete the printer from Printers, uninstall any HP printing software
(if any) in Control Panel, and possibly delete the printer from Device
Manager, if necessary. Physically disconnect printer data cable (USB or
parallel or Ethernet). Reboot.
Then I would connect the printer without having installed any HP printing
drivers or software. If Vista recognizes the printer and installs driver(s)
as it sees fit, I would test the level of functionality provided by the
Vista-provided drivers. If the printer does everything you need it to do,
I'd stop there, and check for page separator correctness.
If you're still getting a separator page at that point, then I would start
searching HP Help and Support.
My three-year-old HP 2300 monochrome laser printer was recognized by and
auto-installed by Vista, but one feature of WordPerfect (shrink to fit)
didn't work correctly with the PCL5 driver installed by Vista. I downloaded
the PCL6 driver for the HP 2300, and am very happy with its full
functionality, features and print quality.
Let us know where you are on this.