hello...
you could try the old "repair permissions" route, but it sounds like something has just been corrupted somehow - os x doesn't have a rollback feature on the system, so you could try any of the following:
- delete your finder preferences - a good how-to is here:
http://www.thexlab.com/faqs/finder.html
- run disk warrior if you have it
- consider re-installing :-/
but i would definitely start with removing your finder prefs...
sitruc