Switching y and z on macbook pro

I want to switch the keys y and z on my macbook pro.. So than when i will press y it will type z and when i press z it will type y.

I tried with the: system preferences -> language & text -> text -> and added the replacements but it does not work.

Please help me.

I already found the solution so you can close the thread.

Solution: KeyRemap4Macbook