Originally Posted by a nonymous
You click the button to the right of the Quote button, it looks like a piece of paper with a quotation mark and a plus sign on it, it says Multi-Quote This Message when you mouse over. Do this for the 1st post you want to multi-quote, and then on the second, hit the Quote button. If you want to do more than 2, just multi-quote all but the last (and hit Quote on the last).
For future reference, this type of question doesn't really go here. Probably goes in About the Forums (where this has actually been discussed before).