Matching multiple columns

I searched for awhile but haven't quite come up with a solution to my problem. Using Excel 2007. I am trying to find matches on two different sheets using 3 columns of data on each sheet. The sheets arent aligned because one sheet may have more info on it than the other. I attached a small example of what im talking about to help describe my problem. I need to find exact matches using "data 1", "data 2" and "data 3" on "Set 1" with the same on "Set 2". As you can see I have to use multiple columns because there may be duplicates in "data 1" but their other variables don't match. Once the match is found I need to compare(subtract) the column "data 4" from the matching pairs, but at this point im more concerned about trying to figure out how to match using the multiple variables.