It would depend on you current level of activity. I enjoyed P90x and found the weight portion of the training was a bit more aerobic then I expected. You typically move between sets fairly quickly so it was not like my typical weight workout.
It all comes down to how hard you want to push the P90x. It is a good work out but like all workouts you control the intensity. You can do it without breaking a sweat by cheating moves or using lighter weights or you can attack your body and make it hurt!
If you are currently pulling an hour of cardio in the am and an hour of weights in the evening, you most likely could still do the cardio and P90x in the evening. I would cut the cardio back to just half an hour for the first few days to see how you handle it. On plyo days...you may want to easy cardio that morning.