I have found that HP scanner software is particularly fussy. When you log in the software tries to find a scanner immediately. If it doesn't find one on the USB chain, it complains. I dismiss I then the complaint. When I want to use the scanner, sometimes I have no trouble starting up the software and getting it to recognize the scanner. Other times I have to turn on the scanner first, then open the software... other times I have to unplug the scanner from the USB chain, and plug it back in. I have found no way to bypass the initial handshake when I log in, nor the magic bullet that would just allow the scanner to operate without all the bells and whistle button software that is part of the scanner package... But it all works in the end. If Leopard broke it I'm positive that HP or Apple will fix it. I was looking at your scnner in the store, and would consider buying it. The price is right, but my 4570c is doing just fine.