Click on the last box where edit quote etc is and then just click on Quote message in reply box underneath the quick reply.
Bottom right corner of someones post there is a button called "Quick reply to this message", click on that, then click on "Quote message in reply?" before you post.
Testing Edit: Wow! This is big, this is going to revolutionise the way I post. This is a whole new world.
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LOL <object width="425" height="344"><param name="movie" value="http://www.youtube.com/v/xFEfIddgvDk&hl=en&fs=1&"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/xFEfIddgvDk&hl=en&fs=1&" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="425" height="344"></embed></object>