Knoppix is a Linux Live CD distribution. This means that you can put the CD into your CD Drive, boot off it and have a full linux desktop up and running in less than 2 minutes without touching anything on your harddrive. By default Knoppix will mount any hard drive partitions that it can find in read only mode, so there is no danger of hurting any of your existing installations.
Find out more at 
http://www.knoppix.net/
WLUG has a customised Knoppix CD, see WLUGKnoppix? for more details.
