Yeah... I know it's a little confusing. Let me break it down for you. The memory (RAM) is somewhat of a storage device. We'll call it SHORT TERM MEMORY. You can load samples and sound files into the short term memory to bang out a beat. Once you turn your MPC off, it's gone. If you only have 16mb, you are limited to loading up only 16mb into your "memory". The Hard drive is your LONGTERM MEMORY. This is where you store beats you have made or all your samples. If you want to up your short term memory, you will have to upgrade to the 128mb ram. There are threads on that topic all over the place here, you just have to look. Hope this helped.
There are only 2 things in life that are guaranteed... Death and Taxes. I'm comin' to collect !!