The way I did it is on my Mac with Garage Band. You can just upload a CD (used the disney parks music CD) to itunes, grab tracks into Garage Band, select the parts you want to use (up to 40 seconds) then there is an option to save a ring tone to itunes. If you google creating ringtones in garage band there is a great tutorial on a site called lifehacker.
I'm not sure how to do this in Windows, but there must be a way.
Funny story, my default ringtone is a chunk of Spectromagic. I was just in FW riding around on a golf cart one evening when my phone rings. For about 5 seconds I was amazed that they could pipe the Spectromagic music into the golf carts (that don't have a sound system). I guess it isn't hard to believe the incredible at WDW