The following information uses two Windows guest OSs to describe the procedure of installing multiple guest OSs on a VM.
Create a VM and install a Windows OS on it. For example, install Windows Server 2003 Enterprise x64 Edition.
Shut down the VM.
Add a new disk to the VM for installing a second guest OS (for example, Windows 7).
Mount the ISO image file for the second guest OS in the CD-ROM of the VM, and set CD-ROM as the first boot option.
Start the VM. The VM automatically installs the second guest OS from the CD-ROM.