astroview:
For a while back in 1999 I did use Win 2K Beta RC2 , but I can't remember if I used the HP 812C with that OS - probably not. Because I had trouble using dual monitors with Win 2K Beta RC2, I later went back to Win 98SE. By now, I would hope, there should be drivers available for the latest version of Win 2K and the 812C, but I'm nt really sure. I have never run the 812C with the USB.
As far as using the parallel or USB port goes, I only know what HP told me. Some day when I have nothing better to do I'll do a test of the two modes (and then publish a ridiculously long article about it at AnandTech.

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Here's a copy of my e-mail correspondence with HP:
<<
QUESTION:
My printer works fine, but I'd like to know which gives the fastest printing:
1. USB
2. Parallel port @ SPP
3. Parallel port @ ECP
4. Parallel port @ EPP
5. Parallel port @ ECP+ EPP
My PC's BIOS allows any of the
above settings & I've used 2 &
3 above without a problem.
ANSWER:
Thank you for contacting Hewlett-Packard's Customer Care.
Hi Gerald:
I understand you want to know which port gives the fastest printing.
The ECP port is the fastest port and the one recommended for our
printers. EPP would be the second fastest port, and the SPP port is
the slowest.
Port descriptions:
ECP
ECP stands for Extended Capabilities Port. This setting
allows the computer's parallel port to send and receive data
in both directions simultaneously. This is the preferred and
fastest type of communication available for newer printers.
ECP is the preferred port setting for most HP DeskJet
printers.
SPP, output, compatible, standard, or Centronics
These settings allow the computer's parallel port to operate
in an output-only mode, meaning data can be sent out to the
printer. The parallel port can also receive limited feedback
from the printer. These settings can also be used as the
alternate port setting for HP DeskJet printers if the ECP
port setting is not available.
Standard bidi, bidi, or bidirectional
These settings allow the computer's parallel port to send
and receive data, but only in one direction at a time,
either sending or receiving.
For information on checking or changing the parallel port
configuration for your computer, see the computer
documentation.
EPP is used for high speed read/write peripheral devices, such a disk
drives or CD ROM.
The speed of the LPT and USB ports are as follows:
LPT port: 90 Mb/Sec
USB port: 12 Mb/Sec >>