What OS are you using? Are you using a driver provided by M$, or by HP? On the HP driver, 600x600 DPI is going to be "best" or "normal", and 600x300 or 300x300 will be "draft".
However, the other poster's question must also be answered - why would you want/need to print 300dpi? Are you under the grand illusion that you will save $$$ by printing at a lower resolution? Or are you intentionally trying to create hard-to-read docs?
Making an original suitable for photocopying requires 300 dpi or less. 600 dpi printouts of photos and graphics creat true grey tones and get awfully messy when photocopied. I long for a printer like the old and "unimproved" ones that printed dots instead of greytones.
If anybody has an answer, I would really like to know.