Specifically, HP Scan Pro and Device Manager that came with your All-in-One are not supported in Snow Leopard. Also not supported at the moment is button support, but that will be very shortly (I expect less then a week, but it could be a little bit more).
That being said, you should be able to Scan from the Printer browser (the thing that shows up in the dock), the Print & Fax System Preference, Preview, and Image Capture. Support for all of these applications (and several third party ones) are include with Snow Leopard.
As for importing images into iPhoto, you'll notice from my FAQ entry that if you are trying to import from a card slot on a network device, iPhoto/Image Capture/etc. under Snow Leopard do not support this. The work around is to mount the memory card on your desktop and use the "Import to Library..." option under the file menu. Other apps should have a similar option.
Just trying to help.
Andrew