FWIW: I too was a victim of this problem and stumbled on the cause accidentally. Unfortunately, I did so too late to save myself from the belief that a complete wipe and reinstall from a slipstreamed XPSP2 disc was the only answer. (BTW, I'm glad anyway. My machine is running quite a bit faster now!)
But in my case at least, it is not Divx in general; it is only Dr. Divx. I uninstalled Dr. Divx 105 and left Divx 5.2, and my right-click works fine. In addition, I can encode with Divx 5.2 without crashing either XP or Divx.