One thing I notice is that your query format is wrong. I don't know if it's the only problem (because you said it wasn't even getting that far), but it is a problem.
mysql_query("UPDATE Articles SET headline = '$headline body' = '$body' date = '$date' staffid = '$staffid' WHERE id = '" . $_GET["id"] . "'") or mysql_error();
Specifically, this part:
SET headline = '$headline body' = '$body' date = '$date' staffid = '$staffid'
It should be:
mysql_query("UPDATE Articles SET headline='$headline',body='$body',date='$date, staffid = '$staffid' WHERE id = '" . $_GET["id"] . "'") or mysql_error();
Also notice that if the headling or body has single quotes in them, it won't work. You'll probably want to use mysql_real_escape_string or something like that.