Anticipated PK Violation

I am maintaining a stored proc that does the following (pseudo code for simplicity)


INSERT INTO MyTable (CountColumn, ...) VALUES (1, ...)

-- 2627 = Primary key violation
IF (@@ERROR = 2627)
UPDATE MyTable SET CountColumn = CountColumn + 1
WHERE ...


Basically, try to create a new record with a PK and a count of 1. If a PK violation occurs, UPDATE the count of existing record.

Pretty simple logic. On some servers this works exactly as expected; the PK violation is caught and handled internally. On other servers, this error percolates out of the stored proc and causes the calling code to receive an error and fail. All servers are SQL Server 2000 SP3a Standard Edition. Any ideas why this happens?

Is there a better (and ideally as fast or faster) way to handle the INSERT/UPDATE issue? I can put the UPDATE first and INSERT if @@ROWCOUNT is 0, but that has the slight potential of a race condition where two processes try to INSERT the same PK at the same time.