I need a little help in figuring how to develop a new plugin that will do the following:

this plugin should integrate into links admin so that whenever a link change is validated or whenever the admin goes into links admin and modifies a listing (only certain fields like address, phone # ...) then an email is sent somewhere with only the specific fields (address ...) that were modified.

How would i go about coding this plugin?
do i need to modify admin.cgi for this?

can someone point me in the right direction.

Thanks

Hagai