I encountered a small hiccup while upgrading to Mac OS 10.5: when I first started up after the upgrade, the Finder wouldn’t launch. Other programs would run, but I couldn’t get to my desktop or navigate to any files. Turns out that DivX was to blame. If you’re upgrading, delete your DivX player first and the file in /Library/Application Support. If you’ve already upgraded and the Finder just gives you a beachball, you can do a few things:

  1. If you have another Mac and a Firewire cable handy, plug them together and reboot the affected Mac while holding T. This will restart the computer and mount its hard drive on your other Mac. Open up the disk and go to /Library/Application Support. Delete DivXNetworks or rename it DivXNetworks.prev. Unplug the Firewire cable, reboot your Mac, and you should be set.
  2. If you don’t have another Mac, you’ll have to use the Terminal, which might be hard to get to without the Finder. If you already have it in your Dock or have it in a Stack you can just launch it. Otherwise, you might need to wait for Spotlight to index your drive, then search for “Terminal” and run it from there. Once in Terminal, type:

sudo mv “/Library/Application Support/DivXNetworks” “/Library/Application Support/DivXNetworks.prev”

Then right-click/ctrl-click on the Finder and tell it to relaunch.

More info in this support thread.