I didn't reply at first because I'm not familiar with the P90X, but since no one else seems to be either I'll try my best to explain what you ask, but I cannot make any comparisons.
The Strength DVD is a single full body workout. The force DVD is somewhat split, with a lower body focus day 1, and upper body day 2.
The cardio workout is not mixed in, if you want a workout with strength training and cardio mixed together there is Cardio Circuit and Ropes & Straps.
There is some stretching at the end of the Strength one, but not the end of the force training.
Since you say you are somewhat new to intense exercise you might benefit most from the Essentials bundle, which includes the All Body Express, Essentials: Strength, Flexibility and Cardio Circuit.
The Force trainer is somewhat more intense, but misses out on a lot of what Fitness Anywhere has developed since it was published, such as the stretching components.
Hope that helps,
Max