I love sprinting. Just finished my sprint workout at the track and I wanted to share some, hopefully helpful, tips that make me feel powerful and wonderful. 
First of all: don't spend more than 30 mins. That's about all my body can handle when it comes to this type of intense workout. It may sound like 30 mins is nothing...but if you are truly working at max intensity, it's PLENTY.
Next: MUSIC helps a lot. This song: "Someday" by the Black eyed peas, came on my ipod just before I started. The lyrics are so positive and the beat is up and it just made me feel like pushing myself. I encourage you to use music. It makes the experience so much better. Make sure you use good headphones that will stay in your ears when you turn up the speed.
Last: quit when you are tired. Don't risk injury. You have to be honest with yourself. You don't need to work yourself into wheelchair the next day kind of fatigue, but do put  in a good effort. The results you achieve are a reflection of the effort you put in. 
Good luck my friends. Get out there and spend 20 mins of your day changing your body and your mind. Everyone's got 20 mins to spare, no matter how "busy" you are. This is time well spent, and a small sacrifice for pretty significant rewards.