You may need to define the top left height width of the span.

About background mixed up problem, you may need to change
background.

See
http://meyerweb.com/eric/css/edge/popups/demo2.html
and
http://www.quirksmode.org/css/ie6_purecsspopups.html

for more information.

BTW: the pdmenu has problems in firefox: the list appears on mouse over but will not disappear afterwards.