It's an incompatibility with the QuickTime update. Here's a link to the solution:
http://macosx.com/forums/mac-os-x-system-mac-software/305399-help-blinks.html
The same thing happened too me. The finder crashes and restarts every 1.5 minutes exactly. OS X 10.4.11. Ran Disk Utility, MacJanitor and all seems clean. DiskWarrior 3.0.3 was unable to help.
Console.log showed this:
Mac OS X Version 10.4.11 (Build 8S165)
2009-01-24 16:03:49 -0600
2009-01-24...