Long gym workouts

I think you also want to make sure to do a post-weights cooldown on the treadmill. I remember hearing something about weightlighting causing a buildup of lactic acid in your muscles that can be alleviated by a good stretch or a quick 5 minutes of slow walking

cardio first

I agree with cardio first.  Plus the cardio first will help get you properly warmed up for weights and reduce the chance of injury.

http://eninjatraining.blogspot.com/ 

Unless a client insists on doing cardio and resistance training on the same day, I usually recommend that cardio be done at every workout. Using the routine, the time spent for cardio on days when resistance training is performed is less (approximately 20 minutes). The cardio is done first and because less time is spent, there is ample energy left for a great resistance workout. On the days when only cardio is done, the time can be 45-50 minutes. I give a sample workout in my fitness eBook found at www.fitnessbasics101.com You might want to check it out.

Success to you.