Multipel dropdowns using Ajax

[eluser]shahmy[/eluser]
Hi to all, I was create one of web application. It include student registration form.
It contain three drop down boxes.
1.Grade
2.Subject and
3.Teachers.

I want to know, How can i get particular teacher based on unique grade and unique subject for the grade.

That is, if i choose the grade, The teacher drop down should load teachers for under that grade. And if i choose the subjects from my subject drop down the teacher drop down should re load under particulate grade and subjects.
If any one know,Please help Me.
Thank you.

[eluser]phpserver[/eluser]
What you are looking for is chained selects and a tutorial on that can be found here:http://www.yxscripts.com/cs/chainedselects.html

Assuming you need a database for storing the data,you may wanna take a look at http://sourceforge.net/projects/carbogrid/

Carbogrid has a great roadmap and the feature you are asking is included.