The type of muscle will depend on whether one wants to sprint (as fast as possible) a short distance, e.g. 100 m, 200 m or up to 400 m, vs longer distances like 1 km, 1.5 km and longer.
Sprinters want fast twitching fibers, whereas long distance runners want slower twitching fibers. The difference comes with training, and weight-training is part of it. Also, stretching is very important, and I can't overemphasize that since I have seen runners do serious injury to themselves without proper stretching.
Eat protein or use a protein (amino acid) supplement, but stay away from steroids.
Also, check out -
http://www.pponline.co.uk/encyc/sprinting.htm . I just found it, so I don't know much about it, except it looks interesting. Apparently registration is required.
Also, talk to seasoned runners about their training regimes and diet. See JasonRox's thread on
Working Out and Supplements in this forum.