Regular low-level cardio helps keep your blood sugar under control by making your muscles take up glucose to top up depleted glycogen stores. Walking most days is good idea.
You will benefit from strength/resistance training and a bit of sprinting too. As Dirlot said, you don't need a gym membership for this if you buy a few weights.
F 5 ft 3. HW: 196 lbs. Primal SW (May 2011): 182 lbs (42% BF)... W June '12: 160 lbs (29% BF) (UK size 12, US size 8). GW: ~24% BF - have ditched the scales til I fit into a pair of UK size 10 bootcut jeans. Currently aligning towards 'The Perfect Health Diet' having swapped some fat for potatoes.