Hey
Quite easy really just add the following snippet
rel="canonical" href="Your URL Here" />
This should be placed between the tags of the page.
BUT.......
Make sure you are using this correctly, if you have duplicate page titles due to canonicalisation (http://www.seomoz.org/beginners-guide-to-seo/basics-of-search-engine-friendly-design-and-development) then that's fine but if its just because you have duplicate page titles across your pages then they need to be rewritten.
Hope that helps