The most challenging thing about (re)starting running is not the cardio fitness aspect, but rather the adaptation of your leg muscles and tendons to the stresses and impact of running.
I note that most of the current activities you list are low impact, so it is no surprise that your legs have lost some of their impact conditioning. It is generally recommended that you build up a solid base of walking (ie. 2-3 months) first before starting to run. The moderate impact of walking is good preparation for the legs.
When you do start transitioning to running, I would strongly recommend a Couch to 5K program. www.sparkpeople.com/resource/fitness_artic
Rather than running continuously, these programs work through progressively increasing intervals of running and walking - this not only gradually builds your fitness, but gives your legs time to adapt to the impact.