What causes Autorun to launch on W2K/XP?

The only way I can get autorun media to launch after mounting on my
filesystem is to force a user-mode app to call
BroadcastSystemMessage(DBT_DEVICEARRIVAL). I know this isn’t correct.
But, autorun is not launched simply due to a successful mount of a CD
drive. Does it possibly have to do with a new mount within a specified
period of time after a new media arrival (per cdrom.sys)??

Does anybody now which MS driver initiates an autorun and under what
circumstances the autorun launches?

Thanks!