Hi Janaraja,
First thing Module Pool programs are very much encapsulated to their main program so out side data cannot modify them directly.
Secondly there is no link between your Webpage which is in ASP / .NET and SAP so I am afraid it is not possible.
Well there is one way but am not sure if it will work 100%....
Clear the CLIPBOARD before calling your ASP Page.
And in your ASP page let it pass the selected data via CLIPBOARD.
In your screen PAI keep reading the clipboard till you get a value and update the matnr.
Regards