I too am trying to do that and have met with success. You were on the right track before. Make movie, next to sequence type choose image files and click OK. Then name your file, at bottom of that popup, choose .tif and then click Save. Remember to create a new folder because this will save as many files as you have frames in your animation. Thats it. To check it, go into Photoshop, open up any of the files in that folder and go to your channels. It will show a black field with white area for your poser. That is what you need. When you bring it into a video editing package like Premiere you can drop out whatever is black in your alpha channel. Whatever is white will allow the poser person to show.