Hi Steve,
To answer your questions in turn, yes it is worth visiting a dry slope or indoor snow slope to learn the basics beforehand. You will have a headstart if you know how to put your skis on, step up the hill and maybe stop and turn when you get here. If you have skied on an artificial slope you can join the dry slopers class rather than the beginners. You will be with people of similar ability (after the instructors watch you skiing to match you up)and will progress faster than a beginner group. The children's classes don't have a dry slope group as such, but will be split early on into those who have skied a little and those who haven't. Have a look at the Monday Morning Guide on this site (
http://www.arinsal-andorra.com/content/view/85/84/) for more info on the groups.
As to your second question, the Gondola is the usual way up the mountain, unless you are staying at the Crest, Patagonia or Velvet in which case the chairlift is nearer. However you can walk between the two in 15-20 minutes and there are busses as well. Most classes will use a chairlift at some point in the week, but not on the first day (except for intermediates who start on the chairs). A lot of people are nervous about the chairs but cope with them okay when they get there, and find they are not that scary. Young children have to ride the chair with an adult, so never have to manage it alone.
Hope this helps, look forward to seeing you in the winter,
Ian