What is the difference between using 16 bit (48000 Hz) and 24 bit (48000 Hz)?

I bought a new sound card (X-Fi and I love it!) for my headphones and I was fooling around with the sound properties in Windows and noticed there were different options for the default format: 16 bit 48000 Hz, 16 bit 96000 Hz, 24 bit 48000 Hz, and 24 bit 96000 Hz. I know obviously the higher Hz/bit rate will sound better assuming you have the source, but will I notice a difference if I change it from DVD quality to something else? I use Bose QC 15 headphones to listen to MP3 files purchased from iTunes, recorded from CDs, and purchased from other music stores (they are usually 256-320 Kbps).