Whats a dual/multi boot?

I recently got windows 7 but i really wanted to keep everything installed on my old xp, so i decided to go for a dual boot.
a dual boot is a way of having two operating systems on the same computer, when you turn on your pc you are given a question:
windows 7
or windows xp
i simply select the one i wish to use and then it will boot up in your chosen system.
here are some great sites that can help you with your dual boot:

http://en.wikipedia.org/wiki/Multi_boot
http://www.techspot.com/guides/143-dual-boot-windows7/

Google search

IMPORTANT!

•before you do anything, make sure all of your data is backed up!

•As soon as you have installed your new operating system you should not be useing the internet.
you must first get a firewall running and a good anti-virus program, windows should warn you if you do not have a anit-virus on the computer.

•some programs may not be compatible with your new operator.

•you may need a new disk drive to store all of the operating data on.

•looking into the other operating systems files may currupt your machine.

•sound cards and video card settings may be reset and might only work on one operating system.