How to use auto margin to work in both Mozilla and IE?

Hi CSS expert! I have been scratching my head trying to figure out why my CSS margin auto code is just working fine in Mozilla Firefox but when I view it in internet explorer, it floats left. I have tried to go through the code several times but nothing is coming forth. I have even tried to use clear:both and overflow properties but to no avail. Anyone with knowledge in CSS programming language, kindly help!
