is one computer at your desk not enough?
do you require the amount of security provided with nothing but a new OS?
if the answer to either of the above is yes here's the solution!

Step 1: Case

this part is not difficult ... find a suitable case to house the following components;

4 port usb hub
1~2 usb thumb drives
male to female usb cable - not essential.

when selecting (or creating) a case there are 2 things to consider, these are;

material - metal may short naked electrical components
plastics - are easy to work with

the 2 unused usb hub ports can be used for memory or user interface devices like a mouse or key board so its a good idea to keep these accessible.

Step 2: Electrical Components

the case only needs to contain 2 parts of circuitry, a 4 port hub and at least 1 usb thumb drive (1GB or higher)
you may have to remove the plastic housing of the hub and memory sticks to be able to fit!

hook it up as the picture shows and insert it into your case!

Step 3: Software Download

depending on the amount of space on your chosen thumb drive you will have to select a operating system.

i recommend Damn Small Linux (DSL) for drives of up to 4 GB and Ubuntu for drives of 4 GB or more.

links:

lucid puppy (dsl build) ................ http://puppylinux.org/main/Download%20Latest%20Release.htm
Ubuntu............................................ http://www.ubuntu.com/download/ubuntu/download - download recommended version!

Step 4: Software Install

simply burn the selected iso to your thumb drive using the program of your choice!

BIOS
before this OS will boot it is essential to rearrange the boot order of the PC you wish to use the drive with.
enter bios by using the default start up key (dependent on machine and bios version) and ensure usb is in the first boot slot.

Step 5: After Thoughts...

at this point in time you have three available usb ports on the hub, these could be used for;

mice
keyboards
Linux compatible usb dongle/wi-fi antenna
extra file space in the form of thumb drives or external hard drives

the possibilities are truly endless so be creative!

PDF of these steps... https://www.instructables.com/pdf/A-pc-within-a-pc/A-pc-within-a-pc.pdf

done!