In my experience, SuSE is pretty straightforward to use. The KDE desktop (default choice) is similar enough to Windows XP that an average user can get going very quickly. As an example, my 6 year-old son sat down at SuSE 10 and was able to browse (we use Firefox on both Windows and Linux), create OpenOffice documents and more without much trouble.
You will probably need to look at your printing and file serving infrastructure and make sure it's working for Linux clients -- but that's an issue for you, not for users. The file manager in SuSE is similar enough to Explorer that learning it isn't much problem.
This was first published in June 2006