Question- Please HELP !

Hello,

I have a php file with embedded html and javascript.
The form has two text fields and one pop-down menu. I have to check the textfields for 1) not empty, 2) not zero, 3) not out of range.

Also depending on the values of the first two textfields I need to populate the pop-down menu from database (Oracle).

I can submit the form to itself to get the values, but then I m not sure how to go about it...

Any help is appreciated.
Thanks