So, Linux sounds interesting. But you don’t want to go to the trouble of installing it onto your hard drive. No problem, get Knoppix.
Knoppix is a Linux distribution which fits onto a CD, which you boot from. It’s also useful if you use public computers, as there is no need to install anything. (Although, I read one anecdote of a school teacher yelling about the student putting a virus on the computer!)
Last but not least, it can be used as an emergency boot disk.