Search a phrase using Spotlight
From the Mac OS X 10.5 Help


  Use quotation marks around text to
  search for exact phrases — the same
  way you do with most Internet
  searches. For example, enter “trip to
  France” in the search field to find
  items on your computer that contain
  that exact phrase. If you didn't use
  quotes, the search results would
  include items that contain any of
  those words.