
I let it do that for about 5 minutes. I turned it off with the power button. I did everything! From zapping the PRAM to repairing disk permissions. I poked through the Apple Support Forums. Finally, I realized that I had installed Norton Anti-Virus (my ISP gives it out for free), and that I should try removing it.
The easiest way to do this is to use the Symantec uninstall utility, which can be very hard to find. For those who are having troubles, I finally found it here: RemoveSymantecFiles removal utility.
Once Norton was removed, my system booted normally.