Primary Key

Let's say that someone trying to insert a record in the primary key which already exist...
it returns an error, and in fact that error:

Error Type:
Microsoft JET Database Engine (0x80004005)
The changes you requested to the table were not successful because they would create duplicate values in the index, primary key, or relationship. Change the data in the field or fields that contain duplicate data, remove the index, or redefine the index to permit duplicate entries and try again
How can I replace that error with a friendly message such as "that record already exists"