what your going to need to do is
1. get the amount of rows in the grid
2. Loop through the number of rows ignoring the current row, comparing each column. If a match then do what ever is required.
personally I wouldn't go this way. I'd start by looking into Dataviews and its filtering capabilities
[edit] didn't understand the requirements at first due to scanning text speak[/edit]
Google shpws plenty of examples on this
vb.net Comparing datasets for duplicate rows