I figured I'd try this on my test system and see how much more damage I can do.
I looked in Synaptic and located the 2.6.20-16 kernel update components that were installed (searched for 2.6.20-16). Marked them for complete removal, applied, and rebooted. Looks like everything is running okay now. Default boot is 2.6.20-15 again.
Note: I booted into the previous 2.6.20-15 kernel for this...
EDIT: Auto-Update is not trying to install the -16 kernel again. Nice.