One of my favourite sites for interval training is DJ Steveboy's site. http://www.djsteveboy.com/intervals.html It has some great mixes for training for different intervals of running. A 5k, an 8k and a 10k training programs.

I am currently training for a half marathon at the end of June. Running has really made a big difference in my life. I still remember the first 5k I ever did. It took my 49 minutes. One of the slowest times. But now I'm doing it in 28 minutes.