I had a difficult time trying to figure out the porting/recompiling solution, and this was prior to the nice instructions by tiggerish. I spent a lot of time pulling my hair out on this one. Anyhow, here's a simple solution that worked for me on my Macbook with Iriverter 0.16.
1) Download a "good" version of mencoder such as from here (if you don't already have one):
http://prdownloads.sourceforge.net/m...es20060307.zip
2) Unzip and locate mencoder in the ffmpegX binaries package above.
3) Locate your Iriverter application and right click on it and select "Show Package Contents" (or use CTRL + Click if you don't have a right-click technology on your mac).
4) Navigate down until you find mencoder in the package (Contents/Resources/Java).
5) Replace the "bad" mencoder found in step (4) with the "good" one from step (2).
6) Have a cold one, you're done.
Here's the ffmpegX page if you need more info from there or if you need the updated mpeg2enc file as well:
http://homepage.mac.com/major4/download.html