Hi dansus!
try this build
http://www.64k.it/andres/data/a/AutoMen17.exe
and use the latest build from here (look at cpu)
http://ffdshow.faireal.net/mirror/mplayer/
in this new build i added a check "Thread" if checked it will enable the threads parameter in mencoder
it's optional since many mencoder build i tested don't supported this switch (with CelticDruid build crash if used with FF4)
hope "quicker" news!
BHH