Need to customize Sales Quotation for two formats

Hi All,

I want to change the sales quotation document (print) dynamically while updating. We have 2 format, one for Product Quotation and second one for Service Quotation.I created 2 reports and 2 menu items , not 2 different design on same report.  Based on the value selected from Sales Quotation form > Other > Document title (Product/Service) ,the print out also need to change depending on the value. Can anyone please tell me which class/methods to customize.

Your help will be highly appracited.

Regards,