Go to your settings and click Manage search engines..
The first box doesn't really matter.
The second one is the keyword you type into the omnibox to start the search.
For the third one (the URL) I use: http://www.google.com/search?as_q=%s&as ... ingrts.com
and that's it. Now all you need to do is type your keyword (mine is "spring") then space or tab and what your searching for..
Not much to it, but it sure is handy