Bestselling author of fiction and non-fiction, Harry Bingham, [great name btw], runs The Writers' Workshop. Check out his site http://www.writersworkshop.com/ for helpful advice or his blog: Write. Edit. Seek Literary agent [link below].
Harry supplies ideas and samples of how to approach agents; the complicated way, or the lazy way [his words, not mine], either way, here's a link to a very simple 'Sample Literary Agent Query Letter' ...
Harry makes it look easy - the only other thing you might need, which he does suggest, is a good book!
Also: Join The Word Cloud: where writers meet. [Its free, just register and join in with a large writing community for feedback, forums and updates.
Well worth a look, great advice, articles, workshops [online workshops] and blog. Thanks Harry.