Interactive and Express Mode

Hi. I'm confused about interactive and express mode. I currently have the latest version of Norton Internet Security, but I have a question about Norton Internet Security 2007 that I had running before. It was my understanding that in interactive mode, Live Update would automatically download updates but not install them; you would have to do this yourself, and in express mode, Live Update would automatically download and install everything for you. Is this the case? If I have it in Interactive mode, will important updates and definitions still automatically be installed? I'm asking because I'm not sure I was smart enough at the time to always manually install everything. Also, I have 2007 running right now on my other computer, and it's in interactive mode, yet seems to be up to date all the time without me doing anything. Thanks for any answers.