Forms Data Controls :: Date Comparision In Gridview - Challenging Logic?

I m working in vs 2005 project(Built before 2 years with deklarit and Infragistics) and not using Ajax Update panel instead I m using Ajaxprodll throughout the project and I cannot use the update panel as it requires the huge changes in web.config file and I dont want to play with config file so I keep using Ajax pro dll.On my page there is a tab control in which there are 4 tabs.Each tab contain gridview and each gridview has same number of column.Firsttab is Daily has daily girdiew,Second Tab is Weekly and has a weekly gridview,Third Tab is Fortinght and has fortnight gridview ,4th is Monthly and has monthly gridview.

First two coumn named as Start Date,End Date in all gridviewMy Q1: If user enters the start date, end date should be greater than start date,at the same time the data (period) entered in first row sholud not be repeatedfor second row or third row or any row in the gridview.It is applicable for all gridview .How should I achieve it?My Q2(Logic????): When user enter the start date and end datein first gridview(Daily) that period should not be allowed to enter in the second gridview(Weekly)or third gridview (Fortnight) or Fourth gridview (Monthly) and Similarily if I enter the period for weekly then it should not be repeated in any other gird and soo.on.My Q3:How should I add row at runtime in gridview without postback? My Q4: What should I do to get Dataformat inside the gridview