Step 1: Safety First

It's downright foolhardy to hack plist or other system files without backing them up first. Navigate to /System/Library/CoreServices/Finder.app (or simply Finder if you have Show All File Extensions unchecked in Finder > Preferences > Advanced). Control-click Finder.app and select Show Package Contents from the pop-up menu. Dig into /Contents/Resources and locate default_smart.plist. Tiger's Smart Folders are merely saved search strings, and this plist file defines the default state of a new Smart Folder - or a Command-F search (which becomes a Smart Folder after you press the Find window's Save button). Option-drag the plist file to your desktop to make a copy.

Back up, Jack, for the good of your Mac.