I don't think it really makes a difference in the long run when you take it, as long as you do take it, but it would be ideal to take it post workout since that's when you're consuming the most high-GI carbs in the day.
Assuming you mean whey protein powder, you should take whey whenever you need extra protein in your diet and can't get it with solid food. With that being said, liquid protein supplementation is essential right after you are finished working out in order to get your body into an anabolic state as soon as possible.
You can warm up before a workout doing short, light-moderate cardio to get your blood flowing. Doing excessive cardio during weight training can have adverse effects if you are trying to gain muscle. Do cardio on days you aren't weight training or in the morning (with PM weight training), but remember to give yourself a few rest days in the process.
