Assuming you are talking about your Officejet 6310, Scanning is only supported through the In-OS drivers at the moment. That means you can scan from your Printer browser, the Print & Fax System Preference, Preview, and Image Capture. If you are unable to Scan through any of those routes, the fix could be as simple as deleting and adding back your printer. If this doesn't fix it, let me know.
As for HP Scan Pro, as I said, that is not supported on Snow Leopard. We will have a solution posted for your Officejet 6310 soon that will enable scanning through an HP application again. In the meantime, many threads on this forum report success running HP Scan Pro under Rosetta. I have not tried this myself, it is obviously officially unsupported, but many are reporting luck with this.
Just trying to help.
Andrew