Hire me for your company and I'll soon train them all
Ahem
More seriously, the main point about training people on computer software is that they have to have a use for it day to day, or the skills will dry up from disuse. For example, at one point I was taught a fair chunk about Access, and whilst I could still sit down today and use it, I'd struggle for a fair while until I got back into the swing of things.
So that leads to the big question *why* are you trying to train people on Excel, is there a specific need for your employees to know how to use it, if so what are they going to do with it and that'll suggest what skillset you need to train.
Also, you might be plesantly surprised at what people can learn on their own, chuck 'em a few tasks in Excel and see who comes up with the answers on their own (for example making a flag to indicate whether a customer's balance is over their set credit limit, multiple solutions to that one)