That would work well (blockquote) except by styling that, every time you used blockquote in the blog somewhere (as in, examples when you weren't trying to box it in), you'd have the box style.
You could, however, combine the two. Make style called (whatever) "q":
CODE
border:1px solid red;
padding:10px;
background:#00C;
Then when you wanted to treat blockquoted text as the highlight box, use this:
CODE
<blockquote class="q">This is the special text.</blockquote>
...and if you installed MTMacros and MTTextile, that same entry line could look like this:
CODE
bq(q). This is the special text.
*Lots* of ways to do things in MT...
Cheers,