yea ive heard the usual "sing from your diaphragm" but im still not sure how. from my "reasearch" a lot of people put breathing exercises like "when you breathe, make sure your stomach expands and not your chest." i can do that no problem, but when i try to sing a note it just does not come out right. Im confused
Great question!! 
Check out my answer to this very similar question:
http://answers.yahoo.com/question/index;_ylt=ApwKfqQ3DD3ssyvKUsjnPUDsy6IX;_ylv=3?qid=20100216144821AAHTvKm&show=7#profile-info-QyGe6e55aa
Good luck!!!!! 
Hope this helps!!!