Found this one on our intranet news page. (Seems like there are geeks elsewhere in our company as well.)
Do a two-word search on Google. How many hits did you get back? If you got one hit, you got a Googlewhack. Google, of course, indexes billions of web pages, so it takes a bit of trial and error, but it's possible.
A sample was mentioned in the article I read, but of course, there's the problem. Get a Googlewhack, and post it, Google crawls your site, and now it's on more than one page in their database, and hence no longer a Googlewhack. But there are sites set up for recording your prizes, and seeing what used to be Googlewhacks. www.googlewhack.com is one, and Googling for "googlewhack" reveals tons of mentions of this. Check it out.
To complicate things a bit further, a "pure" Googlewhack requires both words to be in the dictionary. This adds to the challenge, of course, but hey, it can't be too easy, right?