i have to develop a report whose dialog contain checkboxes (1) Customer , (2) Vendor and (3)Cust/Vend . When customer is checked it will give detail of customer and when vendor is checked it will give details of vendor and when Cust/vend is checked it will give detail of both.
As Syed said, get your tables and check boxes, or use the fetch method to fetch the data.
Look at standard reports that incorporate this, ProdPickList report, APMJobTable report are two examples of this, they basically show the sections based on the TRUE / FALSE of the checkbox.
Then in your fetch set up conditions if the Cust check box or Vend checks box is ticked then fire a programmable section that will contain your fields for either cust / vend or both.