custom button in IW32 & hide button in IW28

Hi All,

We have a requirement is:
1) to add a custom button to application toolbar in IW32 tcode and when clicked on this button it has to call a custom transaction.
Could anybody please provide the steps to add the custom button to application toolbar in IW32?

2) to hide button in the application toolbar of IW28. is there any exit to do this?