Quote - Sorry for my ignorance, but is Poser 7 suitable for making an animated short of 2 - 3 minutes with a several characters and story line including action and dialogue? 

Or do other packages, like Cinema 4d, etc add capabilities lacking in Poser?  And if so, do I need to be concerned with compatibility?

Poser should do quite well for a movie like that.
You can look through a number of animation on youtube, made with Poser. It's quite capable.
http://www.youtube.com/results?search_query=poser&search_type=&aq=f

Cinema 4D and other high end software will add capabilities and flexibility, and ability to get a super customized high end look. This high end look is usually a necessity if you;re foing for broadcast quality animation.
For fun short movies, hobby movies, instruction manuals and videos and similar application where high end customizing flexibility is not make it or break it issue, poser will do great.

Also, with the amount of pre-made content, the learning curve on getting to use Poser will be a lot shorter.

If you're doing an amination for your portfolio, to help you with admission to an art and animation school or get a job in TV or movie animation, Poser may not cut it - unless you become an extraordinarily skilled user.

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