Hi Torsten,

If you would like to show a default browser tooltip, that is fairly simple.  You just need to set the 'title' attribute of the cells.  This can be done in the initialize client side event.

Here is an example handler. 

function initGrid(grid, args) {
            var rows = grid.get_rows();
            var rowCount = rows.get_length();
            var cellCount = rowCount > 0 ? rows.get_row(0).get_cellCount() : 0;
            for (var r = 0; r < rowCount; ++r) {
                var row = rows.get_row(r);
                for (var c = 0; c < cellCount; ++c) {
                    var cell = row.get_cell(c);
                    var cellEl = row.get_cell(c).get_element();
                    cellEl.title = cell.get_text();
                }
            }
        }

Hopefully this accomplishes what you need. 

regards,

David Young