Portable virtualization software?

You can use Virtual Box Portable.

As for one that does not require administrator privileges, I am not sure you will find one that is full featured as most (well all) of the virtualisation software I have seen gets their networking via a driver that is installed.

Of course, if you do not want networking, you may be in luck if you delete / do not install the drivers.

I tended to use QEMU with QEMU manager for that. its not as snappy as some of the other virtualsation software but it does networking without the need to install drivers and such. It will probably run perfectly well on a non admin account

MojoPac is an application virtualization product from RingCube Technologies. MojoPac turns any USB 2.0 storage device, such as iPods, USB flash drives, portable hard drives, USB-enabled cell phones, and USB-enabled digital cameras, into a portable computing environment.

MojoPac is freeware.