Attached, a patch for the SD870IS that includes both SDHC/dual-boot and movie_rec support, and also the compiled firmware for testing. I got video compression settings and optical zoom working.
movie_rec may be bigger than it needs to be... there are probably some functions that can be taken out, but I'm not sure which.
I'm officially giving up on mute_on_zoom for the time being; I'm setting the right bit on the WM1400 to turn off the mic but it doesn't seem to have any effect, so the camera hardware probably doesn't support muting the mic...