Make post code text upper-case when someone registers an account

Just a simple mod we created to make the post code text upper case when someone registers a new account on our store, we did this to make it more user friendly when trying to distinguish between different lower case letters eg i,I , l,L, 0,o used in our customers address, might not be every ones taste but we found it much easier with this mod installed Tested on 1.5.4 - 1.5.6.4 but should work with earlier vesions