Prevent duplicates in sharepoint list (Urgent)

Aug 8, 2010 at 10:34 AM

Im using MOSS 2007 and Im new to sharepoint.
I have to create a custom list and want to prevent duplicate value in a particular field. How do I do it. I have used this[^] and it gives error when i re type a field value rather popping up a message or other.
So, please help me to solve this? how do i handle this using event handling???