Apple Store Question

If I go to an Apple Store to buy a new computer will they install more memory and change the hard drive for me to a larger one? If so, do they charge for the installation or will they do it for free since I am buying the computer at the store? I especially want to know about adding more memory. Are there any other specials I should ask the clerk for at the Apple Store that I should know about (free memory, etc.)

I just called Mac Connection (and Mac Mall) and they charge $39.00 to install the memory and another $39.00 to install the Airport card. That would be an extra $80.00 so the sales tax deal is no big deal if my local Apple Store does it for free.

Also, is an 80GB hard drive big enough or should I go for the 160?