How to select table row based upon the contents of the first td?

How to select table row based upon the contents of the first td?

Hate to trouble you gurus with such a simple question but I'm just beginning w/jquery etc.

Anyway i've come up with the following but it doesn't work.
                                    $("#table_id td").not(".Source:contains('System')").parent().addClass('edit_allowed');

The first column has class "Source" and I want to add the class name "edit_allowed" if the contents of teh first td is "System".

Thanks in advance.