P90X is a strength/muscle building program that's in a 90 day format. You can do the program following the classic, doubles, or the lean rotation. They are about lifting heavy and gaining mass and/or strength. You can do a search for it and find TONS of stuff. Many people on this forum LOVE it (although I'm not one of them, if you look on the OD, there's a thread called "Like Cathe Way more than P90X", I say why and so do others). Besides that thread, there's another one from a few months ago called "Everything you ever wanted to know about P90X thread" (I'm thinking that's what it's called). Anyway, it was started by allwildgirl.
Carolyn