Just curious what you all use to convert S3 (or other camera) movies to a smaller file size in order to email/upload?

Someone on another forum recommended Windows Movie maker. Strange thing happened when I used it though. First video did fine. It reduced the file size by an large amount and didn't suffer too much quality in the process. tried to do it with another S3 video and it actually split the video in 2 pieces and both play upside down. The video is perfectly fine just playing in WMP so I think the problem may be with WMM.
Anyone ever hear of such? What do you use?