Booting a live Linux CD/ISO in the VM shouldn't have anything to do with privileges for the Linux OS that is already running. To connect ISO, Edit Settings of the VM, select CD-ROM device, and select Datastore ISO, tick Connected, and Connect at power on. Reboot the VM.
If you want to connect ISO from your client (desktop) machine, select Client CD ROM in Edit settings. Reboot the VM, press Esc when BIOS POST screen comes up (easier said than done). 
Click the CDROM binding icon and select Connect to ISO image on local disk.
Perhaps you could tell us which ESX version you are on, and what's this virtual appliance?
