Why not install Linux on your old computer when you get the new one?
I like dual booting too, but I get a little nervous messing around with the hard drive's Master Boot Record.
The other possibility is installing VirtualBox (free and open source) and running LInux in a virtual machine to see if you like it. Essentially the whole "virtual computer" exists as a file on your computer and you can delete it if you don't like it.
RE: Why I Use Linux Despite The Occasional Frustration And Inconvenience