you have to get the form franked. for this, take the blank form to the bank. i.e. dont write anything on the form. you have to ask them to frank the form for Rs. 100. you will have to fill up a small form (somewhat similar to that of a DD). They may charge you a nominal fee (usually Rs.10) for the franking.
But before that, you will have to find out the bank and branch which has the facility of franking forms.