numeric data type

I've got the following:

cc_exp_month numeric(2,0)

So that I could input '06', for instance -- however the 0 doesn't make it's
way into the column... I get '6' instead.

I want to constrain this in the db, which is why I don't just use:

cc_exp_month integer

My question: what do I need to do to have the constraint ( two digits ) work,
while still keeping the extra 0?

Thanks.