as crimsonaudio said, P90X is not for beginners, the Insanity work-out even less so (not saying you are a beginner).
I did P90X last year, and it is tough. The plyometrics DVD is a killer. Almost hurled a few times.
But just going through the DVD's is not enough. You really, really have to be meticulous about what/when you eat and drink.
Also, most of the 'after' photos you see on the infomercials are after people went through the course several times, not just one 90 day cycle. I went through two cycles on P90X and burnt myself out. Probably more from hearing Tony Horton for 180 days in a row..hahaha.
But before you buy anything, I'd ask around, chances are someone's got P90X DVD's lying around that they are not using anymore, or you can cycle with them since there's like 12 in the whole set. That could save you some $$$.