I finally got it figured out. My problem was that I deleted some "bloatware" files that, for some reason, are essential to have in order for the update to run. Assuming you did the same thing:
If you haven't already, use Z4Root to root your phone and then install the recovery app found in post 83 here:
http://xdaforums.com/showthread.php?t=875233&page=9 . Run that recovery app in Recovery Boot mode, select Backup, and let it create a nandroid backup of your phone. That backup will end up in /goapkrev/backup on your SD card.
You'll need to download the ROM from post #39 on this page:
http://xdaforums.com/showthread.php?t=880813&page=4 Unrar it, then copy the folder containing 4 files into /goapkrev/backup on your card.
Run Recovery again, but this time select Backup & Restore - Advanced Restore. Select the folder you just copied to your card (2010-12-31.15.54.38), then select Restore System and let it run. That will leave your apps and data untouched. After the restore, select the option to reboot the phone.
Download and install the update, then reboot.
After rebooting, you can re-root using SuperOneClick found here:
http://xdaforums.com/showthread.php?t=913709 Don't forget to enable USB debugging first.
So far, so good