Now that I look at the options, it may not. I was thinking that DVD may be an option, or at the least, .IFO or .VOB formats. As a matter of fact, my Default Settings for VideoLan DO include those DVD formats, so maybe this IS still an option for you.
If you uncheck .IFO and .VOB files from your Media Player, 'Choose defaults for this program' it will no longer open DVD movies by default.
Are you having a problem that if you do have a DVD in your drive Media Player is giving your problems? OR are you trying to stop Media Player opening when you put a disc in your drive?