This is an interesting thread since it touches on a rather generic issue - hardware manufacturers seem to have a rather limited support cycle for their products and are not eager to update their software once the new OS appears on the market. Given that there is very little one can do to influence the manufacturers, there are several options available, most (if not all) of them already outlined in this thread. Unfortunately, there seems to be none that would not incur at least some additional expense.
Since you have the Home edition of Windows 7, the XP mode is not available for you. But if you have already purchased a Win2K DVD, as you have indicated, then I would simply go with the dual-boot scenario. Just follow the steps in the
tutorial (use method two, since you have Windows 7 installed already) and it's not that hard.
I would not worry about the fact that Win2K is not supported anymore by Microsoft. However, I would use it only to run that software that does not run on Windows 7, such as things needed to run your scanner, and keep it offline (after getting all the available updates, I think these are still available even though there will be no new ones). This way you won't need to spend money on an anti-virus for Win2K. if you need to share your images on the internet you could always switch to Windows 7 after the scanning is done. This might be less convenient compared to running just one OS for all purposes, but then you would need to purchase a new copy of the Photoshop and from what I understand something to actually run the scanner - I am not sure, if Photoshop can handle that part as well (Nikon software for the scanner does not appear to get updates for Windows 7).
Finally, there is indeed free graphics software. But, if you have an older scanner, you need something to run it and here GIMP and company won't help you. They can be used for working with the scanned image, but let's face it, they are not as capable as Photoshop. Of course, I don't know your skill level or your intentions, for some tasks GIMP is quite sufficient, for others Photoshop is necessary.