Windows Vista Auto Play Feature.

AutoPlay is a Windows feature that allows you to choose which program to start when using different kinds of media, such as music CDs, movies or DVDs containing photos, etc.

Example, the first time you try to play a music CD, if you have more that one media player installed on your computer, the autoplay feature will ask you which media program do you want to use.

You can change AutoPlay settings for each media type.