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.

Also the data columns arent lined up perfectly like that, there may be other unused data columns in between them and they may not be in the same order(i.e. Set 1 may be data 1, data 2, data 3, data 4 and set 2 could be data 3, data 2, data 1, data 4.