Yes, you are trying to use a trigger when you should be doing this test prior to doing the insert.
IF NOT EXISTS(SELECT 1 FROM SomeTable WHERE whatever test you use) Begin
--Do your insert
End
This is certainly not a good use for a trigger.
Michael L John
If you assassinate a DBA, would you pull a trigger?
To properly post on a forum:
http://www.sqlservercentral.com/articles/61537/