Replacing doors should be no big problem, but, like anything else, there a few things to consider that may not be obvious to a new DIYer when coming up with measurements for the new doors. This is covered in Herrick's book.
The book is excellent and I recommend it to anyone who is condsidering refacing, even if (actually especially if) you planing to hire a professional. Unfortunately, there are a few scam artists out there, and the best defense is an understanding of the what is involved in a quality job. The first portion covers many options and possibilities for refacing, the second section is tehnique. If you have no interest in DIY, you can ignore the technique section.