Changing the column width in a DataGrid

I have an Datagrid that displays a number of columns of
data. I want to allow the user to change the width of
each of the columns as they need to. When the
application runs, the user can modify the width, but
after all the events have fired and the grid is presented
back to the user, the column is still presented back with
its original width. Am I missing something or am I
somehow overriding the user's column width change????