There is no such thing as "versus" and it is not anything that you don't know yet. Grid computing is an engine on a chassis, where cloud computing is a complete car that you drive on. Hence, grid computing is how data is distributed in heterogeneous fashion skipping geographical constraints, while cloud computing is how data is accessed. So the complete product is all these things working together. End of story.
And, yes, it has been around for last 20 years: "The Network Is The Computer", if you still didn't noticed...
