Comparing rows between two sheets

[SpaceShuttle]

Greetings!

In an Excel workbook, there are two sheets, SheetA and SheetB, each of which are made of two columns and thousands of rows of numbers. SheetB needs to be compared against SheetA, and the differences to be shown in SheetC, as in the simplified screenshot here: http://i49.tinypic.com/28txtl1.jpg

Which Excel formulas and methods can do this? I've searched the forum and found some interesting ways to use the array functions, but couldn't figure out how it can apply to my case.

Regards.