You could save the image as a .PNG file. This has transparent background, so it's possible to add your background in Photoshop or Paint shop pro. Try to use a similar background colour to your background image. Poser does a pretty good job anti aliasing, but obviously if you render on a black background, then paste the render onto a blue & white sky for instance, you'll get an outline. I find doing it this way gives you much more control also, as you can render differnt objects with differnt lighting if you wish, save them as seperate renders, then layer them and add pallete changes, blur etc

See below:

Hope this helps.