Both Avid and After Effects will import PNG files sequentially and make a clip with a transparent background.  When you output your animation from Poser choose Image Files rather than AVI files.  Poser will output numbered PNG files and you'll end up with a folder with PNG images numbered sequentially.

When you import into Avid or After Effects, you import as a sequence and the system will automatically created a clip using each PNG as a single frame in the sequence.  This clip has a transparent background.

Your problem my be you using a low end editing program that doesn't support Alpha channels.

There is no need to go the greenscreen route in AfterEffects as the transparent clips self key and save a lot of time.  It's especially effective when you use motion blur - no green fringing, the transparency is perfectly preserved.