I was just about to post a thread on this...
Having the same problems here...
VueScan is not universal yet as listed here:
http://www.hamrick.com/
Though it says it works with Intel-based macs, it hoses up on my Core Solo mini.
I think this might be due to the drivers supplied with the scanner because the scanning software from HP does the same thing, called "Image Zone."
The scanner does show up in the Image Capture device browser, but fails to connect.
Again this leads me to think its the drivers causing the problems.
If only I knew a little more about how the drivers work...