To show u my idea, the image:

Let me explain u now what I wanna achieve w/this. This is suppoustly a request product page, where a customer choose what product ask to some company X by chosing him/her it using the combo box (or list/menu).
Now, I'm stucked 'cause I dont know if what I wanna do is possible or not.
Let me explain u this pretty clear so that u get the idea:
In the picture above I pointed (w/red arrows) the 3 fields in my form, w/their respective form element names (prod_name for the combo box and prod_price and prod_qty for the text fields). What I wanna do is once a product is chosen from the combo box the price of the product, appears inmediately in the text box "prod_price" (located at the right side of the product), of course the price would be taken from a MySQL Database as well as is been taken by the combo box to show the product name.
It is possible to use the variables of one form, before they have been submited????
Thx in advance for any suggestion.