Ideally, you need an install disc. Try looking on eBay.
It is possible to get into Disk Utility from the dock (the dock is a completely separate application from Finder), but that will only allow you to fix permissions on the startup disk; it won't let you repair anything that's been corrupted.
It may also be possible to trash your Finder prefs, either via the dock or the command line. I'm no Terminal expert, but I believe the command is 'rm' to remove a file.
A quick scan of my system shows Finder prefs located at:
Removing a prefs file forces OSX to create a new one, although I'd proceed with caution when deleting anything inside the System.