For archos I use mencoder, works like a charm:
(NOTE: replace <file_in.avi> and <file_out.avi>)

Code:
mencoder -ovc xvid -oac mp3lame -vf scale=320:240 \
-xvidencopts bitrate=128 <file_in.avi> -o <file_out.avi>
Example use:
Code:
mencoder -ovc xvid -oac mp3lame -vf scale=320:240 \
-xvidencopts bitrate=128 video.avi -o test.avi

For PSP I use currently, guide from http://news.softpedia.com/news/Conve...tu-67806.shtml

Which I've created pdf file from the article, if you are interested you can find it here:
http://www.mediafire.com/?xyumx40xmfj


I wan't to use mencoder to due the same thing, but did not have any luck. If you know how, please reply.