How to load a string(which I select) into SAP from a webpage?

Dear SAP Experts,

I designed a SAP screen with a text box and a push button using module pool pgm. when I click that push button (i.e. in PAI), it should generate some static URL of an aspx page (.net) in browser. Since that push button generates that URL we will get the popup browser window with that corresponding aspx page. In that web page I will select one value(MATNR), that value should get filled in my text box(MATNR) which I designed in SAP screen using module pool programming.

Thanks in Advance.

-Janaraja