This is probably what you were looking for:
http://www.tmpgenc.net/

A new commercial version of the TMPG Encoder software has been released, but the freeware version is still available.

As darkphoenix says, the final size of your video (in megabytes) depends upon its resolution (width x height) and whatever compression you're using.

Poser defaults to no compression, so the file size can get large very quickly. I normally use a lossless compression scheme when outputting from Poser; it typically makes the files about 30-50% smaller, and it doesn't affect the quality of the image at all. After I've finished editing the videos in Premiere or some other utility, I'll compress to MPEG-1; this is a lossy compression scheme, so image quality suffers, but it can really crunch the file size.

For instance, my Sabrina dance video (timed at ~34 seconds) is about 225MB uncompressed. If I use lossless Huffyuv compression, the filesize is only 62MB (it was a simple scene, so compressed particularly well). After postwork and editing (colour correction, mostly, and adding music), I converted the video to MPEG-1, using TMPG Encoder. I set the video bitrate to 400Kbps (50 kilobytes per second) and audio to low-fidelity 64Kbps (8 kilobytes per second). This comes out to 58KB per second, or about 1.92MB for the entire 34-second video.

Remember, that one was a very simple scene (one character against a white background), so I could get away with such low settings without the resulting video being compressed into a blurry, pixelated mess. Complex scenes need higher bitrates to maintain image quality.