I think this message from HP's website is pretty definitive:
"We are sorry to inform you that there will be no Windows Vista support available for your HP product. Therefore your product will not work with Windows Vista.
If you are using the Windows Vista operating system on your computer, please consider upgrading to a newer HP product that is supported on Windows Vista. HP has numerous products on the market that support Windows Vista."
I mentioned such a phenomenon when I responded to the Mustek sticky at the top of the Tech forum page. Manufacturers switch off tech support after a certain amount of time, and they generally pull the plug when continuing development is a losing proposition. Like dot matrix printers and floppy drives, there comes a time when companies realize developing and supporting an increasingly obscure product doesn't make sense to their bottom line.
In as few words as possible: Lose the Vista, lose the scanner, or get a Mac (OS X accepts any scanner that's TWAIN compliant; that's how my Epson Perfection 1250 survived for 7+ years). There's no Windows workaround for Vista, and you can safely assume nobody's really working on one.
"Once upon a time, the unattainable standard of beauty had to be met by at least one real person. Now in these days of Photoshop, that model doesn't have to even exist." -Vashti Bandy