datagrid calculation column

[jjr0319]

i have a datagrid where one column needs to be based on calculations. the application is a timeline of events, with fields: Step Order, Original Date, Revised Date. Step Order is basically the order in which each step or milestone needs to be completed. Original Date is read-only and is a listing of dates. Revised Date is originally blank, and the column I want users to be able to edit/update, then have a sub routine calculate. here's an example:

Step Order_____________Original Date_______Revised Date
1_____________________1/1/2001__________1/4/2001 -----> user enterd value
2_____________________2/2/2002__________2/5/2002 -----> calculation starts
3_____________________3/3/2003__________3/6/2003
4_____________________4/4/2004__________4/7/2004
5_____________________5/5/2005__________5/8/2005

a user enters 1/4/2001 in the revised date column, and hits Update. the calculations then trigger, first taking the entered Revised Date and subtract the Original Date for that same row from it (1/4/2001-1/1/2001). it then takes this value (3 days), and adds it to the Original Date for all rows preceding the row that was updated by the user.

im not even sure where to start on this one, as im totally new to ASP.net. i understand this is easier to do with the GridView, but im stuck with 1.1 and our servers will not have 2.0 for some time.

any help is greatly appreciated. ive tried several others forums, but have yet to get any answers.

thanks in advance.