I just did the 1st workout, and I did it at a 3 incline, and 3mph, and when I started to run I put in at 3.5mph, and eventually worked my way up to 4mph, its this to slow? to fast? How should I do it??

I would say go by how intense it feels to you. If you're getting your heart rate up and you're sweating you're getting all the benefits. If it's too easy, speed it up, if you're gasping for air and finding it difficult to finish your training sessions, slow it down.

I agree. How fast you can go is a factor of many things - your leg length, your fitness, etc. That's why C25K goes by time. Shan's method will let you know if you're going too fast or too slow.