Just found out that when Photoshop seems to freeze on the scan (it does with my sc 3970 in Panther as well) and you click on the desktop, the scanned image appears suddenly. And when you click on that, you'll return to Photoshop again where the picture actually is. It may help you not to get too frustrated:-) This may work for other scanners too. I found this purely by accident.
I find the HP software highly insuffient when I compare it to my old UMAX stuff, by the way. Quite user-unfriendly and not thought through.