If the reply link is missing on a comment (it does that after the comments get to a certain depth of nesting) then click on the comment's "link" and you'll get a text box you can reply into.
Ah ok, theatrus2 was the only mention of MSP430 in the discussion under userbinator and in the absence of a "How about " in front of "MSP430?" I assumed you meant "What's a MSP 430?" in reply to theatrus2....but then I should've checked the comment times :)