The logic doesn't elude me, but there are practical limits (or so it seems to me) to what can be accomplished with a device like a scanner over a network. How about this as an alternative: you could network your parent's computers together using something like
Network Magic and then share the folder to which scanned images are sent. The advantage of Network Magic is that anyone can use it to share folders and devices (not USB scanners, though, as far as I can tell). So, even if your parents' computer skills are basic, they should have no problem with it. In this scenario, you're mum would scan an image using your dad's computer and scanner (or ask him to scan something for her if he's sitting next to her) and then access the image from her computer. Actually, it's pretty simple to accomplish this using the features built-in to Win2k/XP/Vista but, at least with 2k and XP, I've found things a bit flaky and have had to get my hands dirty a few times to repair shares and things. With Network Magic, connections are stable and if they do break the GUI is simple enough that my wife can sort things out if I am not around.
My final (and quite random) thought: you're mum should still be able to do most of the heavy lifiting involved, if dad is busy on his computer) - she just has to load the negative into the scanner and press a button on the front of it. All dad should have to do is accept the scan...
I need some ibuprofen and strong coffee!
