well, i do have a photosmart c7280 and Windows Seven RC (x64).
i just installed the printer (its connected over network) via the add-printer-functions of Win Seven. that worked flawless.
then i downloaded the full driver-package with all the apps and stuff (it was called 100_228_PS_AIO_02_Full_Net_deu.exe, (1/1 , 198.83M)
for me, deu as in german, would be the same with en or something without any problems) and startet it. the installer finished without any troubles and it printed out a test-page. all fine, no problems. i did not even have to enable some compatibility-mode or something.
but one thing does not work: the scan-software from hp throws up with some error-message that the device is allready in use or something and thus refuses to start. i have no clue what the reason might be, but maybe it just needs a boot with the printer allready online.
another point that i did not try out yet is duplex-printing. under vista and xp, duplex did not work for some weird reason and the hp-support told me to install the printer as a deskjet 990c. i didnt had to print out anything yet and thus did not try out the duplex yet. but i would guess that the problem persists.