Stop Excel from auto formating?

Iam using excel 07 and it is automatically formatting numbers which is driving me crazy. I have to add a special designation number into a cell and the numbers are formatted like this, ##E##. Well exel thinks I am trying to use exponents or something since I am using an "E" so it is trying to be useful and changes the number format to scientific. Well I am not doing that the number is supposed to be for example 52E3 but excel changes it too 5.20E+04. How do I fix this?