I have examples of cell renderers on my blog: http://www.yqcomputer.com/
for the entry labeled "Cell Renderers" and under that there is a CheckBox
renderer. You should be able to substitute your RadioButton.
If you are planning to have each row of the grid have a radio button and that
checking one of these unchecks the rest in the grid, you may run into a
problem. The cell renderers are re-used as the user scrolls through the grid.
For example, if you select the second row of the grid, then everything else
must become unchecked. When the user scrolls the grid, he should not see the
second row still selected since it represents a different data value. You will
need to make sure the setValue method of the cell renderer knows whether or not
the radio button should be set or not.