[EasyFind|http://www.devon-technologies.com/products/freeware/index.html] can do this, though it's a lot slower than Spotlight.
You can probably do it in Spotlight as well, but I think you need a "Raw Query" search, which is pretty clumsy. I believe that the Spotlight/Finder "friendly" interface implicitly uses all three of these search modifier options listed in Apple's [Spotlight Query Programming Guide|http://developer.apple.com/library/mac/#documentation/Carbon/Conceptual/S potlightQuery/Concepts/QueryFormat.html]:
!http://i51.tinypic.com/2vngp37.jpg!
.
The standard search options don't provide for changing this, but a Raw Query search which uses just
dw as the modifiers instead of
cdw should be case-sensitive. To set this up you could start with a Finder window, type command-F, set the search scope at the top to "Contents, set Kind to "Other" and choose Raw Query, then enter the following in the text entry box:
-----------
kMDItemTextContent == "THIS TEXT AS IT APPEARS HERE"dw
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I've tried this in Snow Leopard and it seems to work - I don't have a Leopard system to test it on. You could substitute any string of your choice between the quotes, and can include wildcards by using the * character. Having to enter "kMDItemTextContent == " is clumsy, though, and EasyFind might be a better choice.
