ASP:drop down box prob

[RusH]

here is the prob: i have 2 drop down box
1. name box1 value : 3,4,5,7,15
2. name box2, the value of box 2 is depend on which value being selected in box 1.
ex. if box1 value = 7 then box2 value=3,4,5
if box1 value = 5 then box2 value = 3,4
box2 display all the value that smaller then value in box1
how to do that in asp??need help immediately ^^ thx