The default core definitions for the search interface use a [search{...}] filter to find the matches to your input. This filter is, by design, case insensitive.
However, if you replace the [search{...}] filter with a [regexp{...}] filter, then it will perform a case-sensitive search by default... and, using [regexp{...}], you can search for *text patterns* rather than just literal text strings.
To change the TW core defaults, you can edit the following two shadow tiddlers:
$:/core/ui/SideBarLists
replace "search{$(searchTiddler)$}" with "regexp{$(searchTiddler)$}"
$:/core/ui/DefaultSearchResultList
replace "search{$(searchTiddler)$}" with "regexp{$(searchTiddler)$}"
AND
replace "search:title{$(searchTiddler)$}" with "regexp:title{$(searchTiddler)$}"
That should do it.
enjoy,
-e
Eric Shulman
TiddlyTools: "Small Tools for Big Ideas" (tm)
InsideTiddlyWiki: The Missing Manuals