I'd highly recommend getting some cardio in, use the cross trainer/bike or rower instead of running if you want. Personally I never use the treadmill, I tend to stick to the cross trainer or rowing machine.
Obviously gaining muscle raises your BMR, but I've never seen any evidence that it's possible to target weight loss, so I wouldn't focus on doing ab exercises (unless your after a killer six pack) because it won't do anything for the fat on your belly (well more than other muscle groups anyway)
Most of all, fair play for being assed to get to the gym regularly, and improving your diet.