[jQuery] Matching content

Newbie question. I'm trying to right a selector that matches content
in a definition list. At the moment I have
$("dt:contains('" + a + "')").next("dd:contains('" + b + "')")
which kind of works, but I really want equals rather than contains.
Somehow I have managed to right 80% of a feature based navigation
system in one evening (blimey - jQuery is powerful!), but I can't get
this right!
Andrew