I used to dual boot, but now, for me,
Virtual PC or
VMWare Server is the way to go.
Both are free and both let you run virtual computers from within Windows (and VMWare Server runs from within Linux too). You can install operating systems on the virtual computers (or "machines") and then start, stop, or pause the virtual machines at will. The vms (virtual machines) are saved as one file and can be copied or backed up and then restored later in case something messes up or you just want to start over from an earlier point.
VMWare even provides a mess of
free "virtual appliances" on their website, which are essentially pre-installed and configured virtual machines running different distributions of Linux configured for different purposes (i.e. a Fedora web server running Apache). You literally just download the vitrual appliance into the correct folder, open up VMWare server and press "play" and you're up and running.
Both products can run multiple vms (the number depends primarily upon how much memory you have and how fast your processor is) and the vms can all "see" each other & communicate on your network (if configured properly) as well as "seeing" & communicating with the host machine and the rest of your network.
For trying out new OS's or practicing working with new programs it can't be beat. And when you're done just delete the files from your hard drive, no re-formating or partitioning or anything.