Hi,
Try reinstalling VLC - latest version is 1.3
If you want to use another player run that program and then use it FILE menu to naviugate to the DVD.
Also you can set the default associations
How to Set Default Associations For a Program in Vista
http://www.vistax64.com/tutorials/83196-default-programs-program-default-associations.html
And check Control Panel - AutoPlay
Hope this helps.
Rob - Bicycle - Mark Twain said it right.