I've used P90X - it's really not for beginners, so it would depend on the shape you're in.
Personally I found it on the boring side (but a lot of people like it) - its *definitely* very intense.
You might find you'll have better results (no matter what level you're at) with Chalean Extreme, also from beachbody. I have it - love it.... didn't keep up with it due to summer/housefull of everyone, but I'm going to restart shortly.
I was first introduced to Chalene Johnson with the Turbo Jam dvds - love love love them and got great results (lost 13" and 9 pounds in the first 10 days). I go back and forth with TJ whenever I can squeeze in the time to work out - they're the most fun.
But if you're looking for strength training, AND don't want to be bored to tears (you seriously need to add your own music to p90x if you do get it) - Chalene Johnson kinda puts her turbo jam music/twist and a few of the moves on her Chalean program.
btw - I felt nauseous VERY quickly on P90X and at the time, I HAD been working out regularly. After about 3 weeks of doing P90X, my hubby asked me what was I doing differently? So I asked him why?
He said because I seemed down, depressed/miserable all the time which he knew wasn't like me, he said he was used to me acting goofy when I did turbo jam, he knew I'd changed something.
Also - in the time I did P90x (almost a month - then went back to TJ) - I actually gained a few pounds, not lost, and didn't notice any real difference in inches lost.
If you haven't seen the infomercial for Chalean Extreme, you can go to youtube and watch it in 3 parts.
If I'm allowed I'll post the urls here, but if they are removed, simply go to youtube and type in Chalean Extreme infomercial. (I don't get anything for it, its not an affiliate link - just a happy customer).
Part 1 -
http://www.youtube.com/watch?v=knXfq87QnOoPart 2 -
http://www.youtube.com/watch?v=PL9dgXKha68Part 3 -
http://www.youtube.com/watch?v=Ufr3aiKmXxUHope this helps