I've compiled both MEncoder 1.0pre8 and the latest SVN trunk version. So when you encounter an problem that is likely to be caused by MEncoder itself, you can try reverting to the earilier 1.0pre8 which is more stable.
Note:
Choose to download i686 version only if you use a non-SSE CPU. In most cases you don't need this.
Download from SourceForge release page