Ignore Duplicate Primary Keys

I have one table that stores log messages generated by a web service. I have a second table where I want to store just the distinct messages from the first table. This second table has two columns one for the message and the second for the checksum of the message. The checksum column is the primary key for the table.

My query for populating the second table looks like:
INSERT INTO TransactionMessages ( message, messageHash )
SELECT DISTINCT message, CHECKSUM( message )
FROM Log
WHERE logDate BETWEEN '2008-03-26 00:00:00' AND '2008-03-26 23:59:59'
AND NOT EXISTS (
SELECT * FROM TransactionMessages
WHERE messageHash = CHECKSUM( Log.message ) )

I run this query once per day to insert the new messages from the day before. It fails when a day has two messages that have the same checksum. In this case I would like to ignore the second message and let the query proceed. I tried creating an instead of insert trigger that only inserted unique primary keys. The trigger looks like:

IF( NOT EXISTS(
SELECT TM.messageHash
FROM TransactionMessages TM, inserted I
WHERE TM.messageHash = I.messageHash
) )
BEGIN
INSERT INTO TransactionMessages ( messageHash, message )
SELECT messageHash, message FROM inserted
END

That didn't work. I think the issue is that all the rows get committed to the table at the end of the whole query. That means the trigger cannot match the duplicate primary key because the initial row has not been inserted yet.

Does anyone know the best way to do this?

Thanks for your help,
Drew