Want to tailor the Finder's Find (Command-F) window? Copy the following into TextEdit, make it plain text, and save it to the Desktop as default_smart.plist:
$ cd /System/Library/CoreServices/Finder.app/Contents/Resources
$ sudo cp default_smart.plist default_smart.plist.bak
The first command changes to the proper directory, and the second one saves the original default search file, so you can restore the current behavior. Enter your admin password at the Password prompt when asked. To activate your modified search box, use this command:
$ sudo cp /Users/username/Desktop/default_smart.plist default_smart.plist
Replace username with your user's short username. To return to the original file, cd to that same directory in Terminal, then use this command:
$ sudo cp default_smart.plist.bak default_smart.plist
[robg adds: You'll need to kill the Finder for this change to take effect. We've covered this sort of edit before (1, 2), but this one adds the 10.5-specific ability to search system files.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20080229204517495