Sorry, this no longer works since Google changed their CSE from API 1.0 to API 2.0. I have tried various search options but the comments are simply not in a static form that is searchable. It might be possible to search google cache (maybe).
Although the blogger bar at the top of the page lets visitors search for content on a blogger blog, there are times when it would be useful to be able to search the comments too. This is now possible by using Google Custom Search.
To set one up go here:
http://www.google.com/cse/
Follow the process through and select the default settings.
When asked to enter the URL of the site to search enter your blog address like this with /* after it:
something.blogspot.com/*
(Where something.blogspot.com is your blogger blog address.)
Note: Setting up the custom search may not be possible from behind some company firewalls and show an error.
Follow the process through and when it is complete you can then either link to the custom search page or embed the supplied code in a page in your blog. Click here to see the one I made for this blog.