If you click on the icon in the menu, you'll reach a page where you can do a google search of this blog only.
I used Import OPML... to add Dave Winer's default outline template into my named outline.
I then changed the "Outline" headline to "Search This Blog" and added a type=html attribute (as well as name=search).
I removed extraneous sections of the template like the rules (which show up as visible text in html) and the footer.
Went to google.com/cse to create a custom search engine for blog.jeffreykisher.com. Copied the code.
Replaced the bodytext macro in the template with the google code surrounded by div tags.
Linked the search icon to /search.
If you want the opml code, grab it here. Just make sure to swap out my search engine with your own.