Below is a link to a great short article by Mark Rippetoe, the author of this excellent book, which I think I've posted about and also given many copies out.
Here is the article which takes five minutes to read. Funny, his comment about getting off the toilet - that's why I'm lifting weights three times a week.
Lighter weights and higher reps. Same effect, less risk, lighter is safer and more reps make up for the lighter weight, right?
Wrong. Hit the link.