Duplicate field value in Trigger

I have an Integer field created (Integer_fld) and would like to create a trigger that checks for duplicate values for previous created items items.

I tried a script from a previous discussion, but could not make it work.  I thought I would start a new discussion for this.

EXAMPLE:

List of Items

ID    State      Integer_fld   Txt_fld

100   Initiate   10023         Some text here...

101   Initiate   10024         Some more text here...

I create a new Item ID 102 and for the Integer_fld I enter 10023.  When I try to save it I would like to see an error message stating it is a duplicate.  ID 100 has the same value in the Integer_fld.

Thank you,

Dan