another simple SQL question

Ok here is another simple question from a novice....

Here is what my table looks like

firstname         lastname         fullname
----------       ----------       -----------
                                              smith, john
                                              green, susan
                                              white, jeff


How can I break the fullname field into firstname lastname fields so it
looks like the following:

firstname      lastname      fullname
---------     ---------       ---------
john             smith             smith, john
susan           green             green, susan
jeff               white             white, jeff

Please let me know. Sorry for such simple novice questions, I appreciate
your support.

THANKS!