In Mail in 10.5 and earlier, converting some text to a numbered or bulleted list was almost impossible: you had to create a new numbered list just above then move your lines into it, then press Return (or use the method described in this hint).
Mail in 10.6 works as expected now: select some paragraphs of text, choose one of the list options, and the text will become a list.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20090919104535518