My core51822's headers have been annoying me for a while. I did get a cable to convert these 2mm pitch headers. Unfortunately (or maybe fortunately) I accidentally killed the board! Whoops. I'll keep this log short since the cable isn't relevant to the project anymore - full details are on my blog.
It's a 44-pin laptop IDE cable. The original connector is 2x24. I sawed it half, mangling only a few of the rows and leaving me with a 2x10 and 2x11 connector. Just right for the core51822's 2x9 headers. The wire is stranded which doesn't play nicely with the breadboard - before using it I soldered a tiny bit of solid wire to the end. I should've bought the longer cable - mine is 2", I should've bought the 8".
Anyway I killed that board so it's on to the next board:
This one is a little harder to find info on but I believe it's a Wireless-Tag WT51822-S2 module. At the very least Wireless-Tag has the best documentation on the chip. I'll put this module on perfboard and try to get an actual functioning controller.