I won't bother answering the first question because it has already been sufficiently answered by others.

I'll tackle part of the question than anban poses though. For an IDS to "see" encrypted traffic you are going to need something like BreachView SSL. I'm not sure how McAfee is doing it, but BreachView SSL is a great product that I highly recommend. They will also work with your IDS vendor to either have BreachView added to the IDS package or they will create a plugin for your IDS if they have access to source code.

As far as catching very small packets... if your switch can see it then your IDS should be able to see it.