Display error message box when some field is empty !

Question

Hi Friends,
I just wanted to display some  error using message box when the required field are not correct....
This is possible in C# windows form using

MessageBox.Show("Some_Field is required");

This can also be done in asp.net using required field validator, but i dont want to use thes controls....
I want to do this wid the above method
 MessageBox.Show("Some_Field is required");
is it possible to do same in asp.net or is there any other proceedure to display mesaage box...

Plz frnd it is very urgent.....if u can help my now...
my wmail id is [email protected]..
Thanks in adv.
Mujtaba