For strictly video encoding and not gaming, probably a 6 core AMD. More cores are better for encoding than raw clockspeed. And the 6 core AMD will be about the same price as a 4 core Intel. For playing games the Intel is better... but since you want to do encoding, grab a 6 core.
The Intel I7 2600K is nice since it has Hyperthreading which can act like it has 4 cores plus 4 virtual cores... but 6 real cores will still be better. And if you wait a little bit for AMD's new chips to come out soon, the price will continue to drop on their current 6 core lineup and that would make them cheaper than the I7.
I usually do encoding using the Cuda cores on my graphics card, but the software I use doesn't do Divx that I am aware of. If you were to encode your videos as MP4 or MKV with the x264 codec, then your CPU doesn't matter if you have a good nVidia graphics card because it won't use your CPU for encoding at all.
But I don't know if ATI or nVidia have anything for Divx, haven't made AVIs or anything for ages now.