Roberts Rules in Plain English by Doris P. Zimmerman and The Modern Edition: Robert's Rules of Order by Darwin Patnode. I found them both for about $5 each at our local Borders.
The entire RRO is something like 800 pages, and you could run a small country with all the rules in that book. Stick with one of the summary versions mentioned, and focus on areas that really apply to PTO: agendas, meeting format, motions, rules of conduct, voting, etc.
It's handy to be able to fall back on RRO when a meeting is going off on a tangent, or a member hogs the floor at a meeting.
There is a book! I forget what edition it is in but I am sure someone will tell you. I personall have Webster's New World Robert's Rules of Order Simplified and Applied, 2nd Edition. I love anything simplified.
