Here's the problem with just jumping into this much running, even if you are already relatively fit. Your bones are not used to this kind of impact (unless you have been doing a ton of high impact exercise already?). It opens yourself up to a host of injuries, including shin splints, stress fractures, etc. Not fun. Much better to work your way up slowly!
I started running with the
couch to 5k program from cool running. It is similar in style to what Annie Mac proposed, and will, gradually, get your body accustomed to running. It still sticks with a 20 minute format, so it may very well appeal to you! There is a relatively new C25k thread here.
If you love it, running is an amazing way to exercise. For me, it has gone much farther than just a way to burn off extra calories. It is a way for me to maintain my sanity and I love propelling my body like that! But, being injured sucks beyond all recognition (says someone who is going on her 6th month recovering from a stress fracture).