Joe Gillespie said:

JavaScript doesn't support multi-dimensional arrays but you can bluff it with arrays of arrays.

I would make a series of arrays of the columns of data so that they are all indexed to the same counter. Then when you get to the last element, reset to zero.

JavaScript arrays are zero-based and you can get the size of the array with the length property.

Have a look at the technique that I've used for scrolling divs (forgetting the fancy jog/shuttle dials) in this month's editorial.

I'd recommend, 'JavaScript the Definitive Guide' by David Flanagan if you aren't up to speed with JavaScript arrays.