Portable Virtual Machine Recommendation?
Solution 1:
There's Portable VirtualBox - found it via this forum post (German forum, little English there.) Readme is included - click the Description folder on the site.
However, do not rely on something like this to be easy to do and/or work properly in all (or most, for that matter) scenarios. All virtualization software requires host kernel level drivers to be present, and that's hard to do portably if you actually want a stable system. See the forum posts for user experiences.
Also, please be aware that running VMs can be very taxing for your flash disk - VMs generate a lot of write I/O.
Solution 2:
Note that any solution you can find will almost certainly be usable only by administrator users, which could hinder you in any corporate environment..
(e.g. I note this quote from the forum Mihai Limbasan linked to: "es geht nur mit Adminrechten." I don't speak German, but I guess that translates as: "It will run only as Administrator.")
Solution 3:
If you are looking for a linux image that is completely portable have a look at pendrivelinux
Solution 4:
There is a software called PortableOS Launcher. It uses Quemu for virtualization and works fine on my school netbook without administrator access. It comes with some open source and free operating systems pre-configured, which you can download straight from the application with wget. You can also configure your own by going to options(6), then os database setup(2), then add and os(1). It opens in command prompt, though. So there is a possibility that it might not be able to run if your administrator has disabled it. You can find out more and download the portable software here: http://portableapps.com/node/21307