Incremented Duplicate URL not wanted

WordPress avoids duplicate URLs by adding an incrementing number to the end of a duplicate URL to make it unique. I don’t want this – I require WordPress to just not create the duplicate post:

I have numerous blogs to combine into one. I am using the permalink structure: %category%/%postname% however I DON’T want WordPress 2.7 to add a ‘-2’ to the URL (i.e. increment) when it discovers a duplicate %category%/%postname%.

Essentially there will be duplicates of %category%/%postname% so what I want it to do is not create the duplicate content – I want WordPress to keep the original post and just not create the duplicate posts.

Assistance will be very very very much appreciated.

Thanks