I think Yuusuke could benefit from a simple breakdown of the grammar. Basically, the structure of it is:
Also note you can contract なければ into なきゃ, so you will often hear in casual conversation something like 食べなきゃ.
It does indeed mean "must."
行かなければならない = I must go.
行かなきゃならない = I gotta go!
etc.
I personally use ならない over いけない, but there's no real rhyme or reason why. As far as I know, they mean exactly the same thing in this situation. If there's a slight connotative difference, I don't know about it.