You would have to transcode one or both of the files. mencoder can probably do it on the fly, but since one video seems tall and narrow 480x640 and one is standard VGA resolution 640x480, I'm not sure what your end product would end up looking like.
You also most likely require a -vf scale filter so the output was all one size. if the fps are different I'd strongly suggest transcoding them separately and then joining the as I can see trying to do that on the fly getting into all kinds of audio sync problems.
You might want to check out "avidemux" (
http://fixounet.free.fr/avidemux/ ) It is a wonderful program that makes working with video a lot easier.
Hope this helps
Freemor