No I don't have THE answer. But, I have an hp6500 e709a with an added duplexer, got it from parts dept where it was on compatability list. It worked fine on two vista pentium duo 32bit laptops and xp upgraded to vista desktop (boy was that a waist
of money) for maybe 4 months then I bought an HP Pavilion with duo-quad Intel and of course Win 7 running 64bit. Now vista machines see it but will only print to the que. Period, no other functions. Pavilion see's it and works on ALL functions I've tried
except it won't duplex even thought it is 'installed' in the printer setup and preferences. Sayes "duplexer not installed" asks permission to print one sided and then flips even pages as if it was duplexing. Have both USB and Network, same problems.
Now, somewhere in their forums HP has said "They are late getting their complete drivers out for 7, but WILL have them online BY the END of January. What's there are currently ONLY basic print and scan drivers." And that is as close as I could get in a month
and a half. Oh, I have a 6 yr old HP Photosmart 2710 on Wireless with a new added duplexer and it has worked without a flaw on ALL my computers, but the ink is too expensive and the speed could be a lot faster, hence the 6500. Hope this helps someone, or
at least helps keep the fire burning under HP's butt.
UP DATE
Last night. 3 hrs after the above post, I got a notice for the up date. Well guess what. I followed the instructions three times. Each time it said I installed correctly, and now I can't even get the the test page past the spooler.
NICE WORK HP! NOT!