i want to hide some dropdown on selection of dropdown.

this insufficient for me .your example is not helping me.now i am trying to explain u my problem again- i wants to design and develop a exactly same from of following link:- http://www.magicbricks.com/post-property-for-sale-rent/residential-commercial but i am facing some problem to identify what is the type of java script is working to hide the fields and displays some other fields on selection of drop down list. please tell me how can i design and develop a new working form exactly like above link's from as soon as possible.