Conditional Format if there is more than one of the same value in the same column

Hi,

Does anyone know which formula to use in the conditional formula, formula box so that the cell will change colour if there is more than one instance of a value in a column?

I.E. if I have a load of values in column B and there are more than one cells which have the value A03D2 in them.

I.E.
A03D2
B10F2
B09E1
A03D2

Then the cells adjacent to both A03D2 will need to change colour.

Thanks in advance,

Regards,

Gary Hewitt-Long