The good thing about linux is, if you need to know something, usually a search on Google will find you an answer. It just takes a lot of courage for people to start using it, but once they do they usually love it because it’s something totally new to them and theres many things to experiment and play with. But becareful with the ‘playing’ part, especially with filesystems. I went through quite a few installations origionally.
As for which distro, Mandrake is good (origionally came from a modified Red Hat), Red Hat is widely accepted, so it’s easy to get help and find info on, Suse has the largest documentation base but Suse is German, so a lot of time seraching for help on Suse will pull you up German docs. Translation is not hard though with some browsers, it just gets a little annoying sometimes. Suse does have a ton of apps though, the last time I used it I think the full install was 10GB.
If I was to reccomend a system for a begginer who wants to learn it, I would suggest Red Hat 7.2 or 7.3, then install both KDE and Gnome. Then once it’s installed, upgrade Gnome to Ximian Gnome (which is very easy if you have a fast internet connection). Ximian has a wonderful package out now with the mail client Evolution. They also have a program called Red Carpet, which allows you to install and remove apps with the click of the mouse. It is VERY easy. If not Ximian Red Carpetn, then the Red Hat Network will allow you to udate, install, and remove packages also. I would definitely check these out. The link to Ximian is http://www.ximian.com