How do you keep track of stacks in live poker?

[Nepthu]

I'm an online player and I am going to be playing live poker in a casino this Monday for the first time. As you are aware, knowing how many chips players have in their stacks is important in no limit hold'em (the game I will be playing). I suppose I could try and estimate by looking at their stacks, but I am afraid they may have high value chips buried in their stack, or may make it may look like a different amount than it is.

Also, if someone asks you how many chips you have in your stack during a hand, do you need to make a response (for proper ettiquete etc)? I don't want to give away any tells through speech. Vice-versa, is it appropriate to ask how much an opponent has left in their stack during a hand, or outside a hand? Thanks.