If I did 20 minutes of cardio before my workout, and then 20 minutes after, will that hurt my muscle growth or strength? I'm trying to lose a bit around the gut, but I don't want to lose the muscles size I have now. I'm not trying to get huge just in shape, you know, a good appearance.
You can still make good muscle gains by doing cardio. But you would be better off doing a separate cardio workout each day rather then combining your weight training and cardio together. To help you lose bodyfat you should do aerobic exercise first thing in the morning before eating. Do 30 - 45 minutes of cardio first thing in the morning when you get up. Doing your cardio at this time will help you burn more bodyfat, your body will resort to burning fat because there is no food in your system to be used as fuel.
By doing a cardio workout in the morning and then later in the day doing a weight training workout you will burn more bodyfat because you are boosting your metabolism 2 times per day. Your metabolism remains high for several hours after you workout, this accounts for a lot of the calories you burn from exercise.
Also, by keeping your cardio and weight training workouts separate, you will be able to lift heavier weights during your weight training.