Poser is NOT a modeling application. It's not impossible to model in Poser, but it's very, very hard to do.
Poser is exactly what the name says it is: a tool to pose existing characters (+ clothes, + hair).

A human character with a frog's head? Can be done. Provided that you have a model of a human character (several models come with the package) and a model of a frog. Individual body parts can be set visible or invisible, so if you set the head of the human to invisible, and all body parts of the frog except for the head (and eyes) are invisible too, you can position the frog head so that it takes the place of the human head.
But actually, this is something I'd do in Max. Take a human body and a frog head, position the head, and match the edges. Then export as .OBJ, import in Poser, and turn it into a figure (not too difficult).
Getting the frog's facial morphs back to work is the toughest job.

As for Max and Vue - there is a (free) exporter from Max directly to Vue, but I do not know if it supports animation. If it does, you could export your animated character from Max to Vue and render the environment and the character in Vue.
But in your case, Vue xStream is probably the easiest solution. Vue natural environments hosted in Max, with camera and light matching. Not cheap, however.

(As a side note, Vue xStream and either Max or Maya was used to create the jungle scenes in Pirates of the Carribean II. We're talking a professional tool here).

The pen is mightier than the sword. But if you literally want to have some impact, use a typewriter

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