Key: SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
Value: 1 restrict to user logged onto console.
Actually this limits access to the INTERACTIVE group. There is a potential gotcha! when this security setting is implemented. If you are logged onto the box and run an install that runs not under your security context but as SYSTEM (some things do install using SYSTEM). Unfortunately the SYSTEM account is not a member of the INTERACTIVE group and thus will not have access to the CDROM. You will have to turn the AllocateCDRoms setting off to give the SYSTEM account access to the local CDROM.