Well now it is possible to install Linux on a Windows computer in one minute.....run all the top open source programs like Mozilla and Open Office and a host of others...access the Windows hard drive etc....All that tedious mucking about configuring thiongs is done automatically as the computer rather disconcertingly talks to you.....
When you have finished and closed down...you take out the disk and you have the tame old Windows computer back....if you really want to go back.
That is how knoppix works. If you have a reasonable CD drive and you can set the computer to boot from the CD drive you don't need to install anything on the hard drive and it works q satisfactorily from the CD...which is of course free.
You can download it from www.knoppix.org or ask me nicely and I will burn a CD for you
My pupils are road-testing this atm so if there are any snags I will keep you posted.