I would point it out at the end of the interview, probably on the way out, depending on how the inteview went. Something like "by the way, I assume you noticed that there are some problems with this code...".

I don't think I would mention it during the interview, unless specifically asked. It would distract from the goal of the interview, namely me ;-)

But then again, I haven't done too many job interviews (as an interviewee) in my life. I have done a lot of interviews trying to sell projects. I'm not sure whether these different types of interviews would require the same skill set.

Liz