I was checking out the Instructables email and I came across this primer for espresso shot tamping by Paige Russell. If you have questions, or what to do it right, I recommend this one. I have read a lot of how-to's across a lot of websites, and this is more or less the same information. However, this one seems to bring all of that together, and skips some of the more esoteric coffee discussions.
Also, it has pictures of someone actually doing as its being described.
Check it out.