How to intersect a shape illustrator cs2?

I have a load of rounded edge rectangles and I want to remove the top rounded part coloured red in picture attached. What would be a quick way of deleting the top red parts. I don't mean the colour red, the whole shape so I am left with half the rectangle from the intersecting line.
I have tried selecting all the artwork and using every command on the pathfinder but no luck yet.

 

Whops, got it, need to use divide and use the direct selection tool after to get seperate items. Sorry