Couch to 5K is a running plan developed to help absolute beginners get into running. The plan involves three runs per week, with a day of rest in between, with a different schedule for each of the nine weeks.
I'm on week four and it's been tough, but a great and free way to improve my fitness.
*UPDATE* - I've just finished the programme (working towards doing the Race For Life) and I feel great - never knew I'd be a runner - couldn't recommend it enough
You can download the podcasts for free and 'Laura' will guide you through your runs.
Good parks to run around include Eaton, Wensum and Waterloo Park, or Mousehold
Couch to 5K Website
More ways to get fit for free