PocketDivx? I hope you mean PocketMVP, it hasn't been called PocketDivx in a long time, so maybe you should update and have better results.
I encode at higher bitrates - 160 is the absolute lowest I'll go, I'm typically in the mid- to upper- 200's and I can get 30fps easily for portrait view, and it will hold 24 (or NTSC 23.98 whatever) in landscape with no problems. Any higher than 24-25fps in landscape though, and the CPU just can't keep up and it gets choppy as frames start dropping.
This is with a 400MHz PPC2002 btw.
Just my opinion, but you're best off not even fooling with WMV for PPC2002 - WMP8.5 isn't exactly the most efficient thing in the world. WMP9 for WM2003 is supposed to be much faster and more efficient.