Multiple Drop Downs

What do I need to put where the red is to make this work?

lists['January and March'] = new Array();
lists['January and March'][0] = new Array(
'01','02','03','04','05','06','07','08','09','10','11','12','13','14','15','16','17','18','19','20', '21','22','23','24','25','26','27','28','29','30','31'
);
lists['January and March'][1] = new Array(

);

I am creating an array so that when the dropdown is used on month that is January or March the next drop down has 31 choices if you choose February then it would be only 29 as well leapyear and all

Or if someone has a good Javascript that does this that is small in size?

http://www.codingforums.com/showthread.php?threadid=21079

Thanks!

I also found one that works great to what I needed

http://javascriptkit.com/script/script2/curdateform2.shtml

lol figures I posted to quick :) but I would still like to know what you would put in the red to make the above work

[edited to remove wrong answer]