Go to Lyle's site and read his stuff on body composition and measuring it. He talks about all the methods and lets you decide which one to use.
This site also has calculations for different number of caliper sites and for the tape measure method:
The Flexible Dieting book goes very well with RFL, but it may not be worth the money for you. Much of the info in the Flexible Dieting book is in RFL, and the rest is available on his site.