If you haven't upgraded to Tiger, you might have missed out one the best desktop search engine provided by OS X 10.4, Spotlight.
With Pocketlight, you can have similar features.
Pocketlight provides search capabilities for Mail.app mailboxes, iCal events, Addressbook.app records and files in a specified folder in Spotlight Style under Mac OS X 10.3.
If you are still using Mac OS X 10.3.x "Panther", you might want to give it a try.
Pocketlight (free)
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