list box

[Denver]

i have 2 list boxes in a form with a subform....
i want that the 2nd list box limits the data after some choices in the 1st
list box, is this possible? Do I need to write code for the both list boxes?
if it is so what would that code be?

my 1st list box name List4 with a ROWSource :SELECT DISTINCTROW [Filtering
Data].[Site Location] FROM [Filtering Data] GROUP BY [Site Location];

my 2nd list box name List39 with a ROWSource : SELECT DISTINCTROW [Filtering
Data].[Drawing Type] FROM [Filtering Data] GROUP BY [Drawing Type];

i have Search button that once click it will filter the choices on the
subform, is this possible.please help me how to start with my codes....

i have Clear button that once i click it will clears all the selection from
both list boxes and show all the datas on subform.....
if this could be possible how im going to write my codes?
I am using access 2003

any help would be appreciated

thanks

denver