Itunes with shuffle and 20GB

From Derby, 1 post

I am thinking of buying an ipod shuffle to use when i go jogging. I already have a 20GB ipod and thus have itunes installed. What I want to know is can I just use the same itunes for both players or is the doftware for the shuffle different.Also if its the same software then what will happen when I plug the shuffle in, will it just copy as many songs as will fit on the memory or will it just wait and let me choose which songs I want to put on it i.e. does it automatically try and update and thus only copy the first few songs due to memory restrictions?

Any help greatly appreciated