Assuming you mean you want to switch to a new row when tabbing from last cell in a row. If so I just posted an example of how to here.
http://www.activewidgets.com/javascript.forum.13490.15/tabbing-from-cell-to-cell.html.
Note that its post #15. Also note that that there are some issues with focus where cell looks like it has focus after tabbing out of grid. I have solution which I may post once I've resolved the click out of grid issue.
If its not what you want I appologize.