Here are some links to pages with more information about platelets:

http://www.ouhsc.edu/platelets/platelets/platelets%20intro.html

http://www.fi.edu/learn/heart/blood/platelet.html

http://www.redcrossblood.org/learn-about-blood/blood-components/platelets

http://www.youtube.com/watch?v=0pnpoEy0eYE

and of course Wikipedia
http://en.wikipedia.org/wiki/Platelet