A really cool CD image is available for NetBSD which boots and runs NetBSD/KDE/KOffice/Samba without using a hard drive.
I am not smart enough to know exactly how it works, but it must be creating some kind of magic hard drive in memory.
I know similar questions have been asked before, but I think they implied using the on-disk operating system. The question is, is it theoretically possible, given enough system resources, to create such a thing with just the OS and a PostgreSQL server installation to use for demonstrating the capabilities of PG to someone who does not want to install it?
ftp://smaug.fh-regensburg.de/pub/NetBSD/life-cd/