My friend told me when having sex think non-sex thoughts and when you feel ur about to ejculate think of a tragic time in your life.
Well, first of all let me tell you that you are not the only man that has that problem, however you can practice with exercises to hold it back and over time you will be able to go for the desired amount of time.
I have found this site, check it out:
http://ezinearticles.com/?How-to-Fix-Premature-Ejaculation-With-3-Safe-Exercises&id=1455237
Good luck!!!