How to dynamically create querystring for a webform call..

I face this problem of making calls to web application and generating dynamic content based on the record selected by the user in CRM.

I created a button on the form. I had a constant url for the web form. I had to extract the qurystring value from the form data values. But special characters and

few manipulation is allowed in the isv.config file. So I created javascript methods in the 'onload' event method of form. 

In isv.config file:

Added Button to the Entity

added "JavaScript="SearchDetails();" attribute of the Button  

function SearchDetails()

{

.. implentation here

.. built dynamic url and made call to web application

}