Would p90x work if I'm trying to put a lot of muscle on or would it just make it harder for me to gain due to the high intensity routines?
Your best chance is to follow the Energy Maximizer (I think thats the name) diet. It's like 75% carbs and will allow you to add mass, but only really works if your BF% is around 8%.
If you're looking to change the composition of you current weight, then I highly recommend P90X. If you feel like you want to gain 10-20lbs in the near future, then this is not at all what you should be doing.