I got the solution by trial & error:
On Page_Load i used to write my HTML string (strHTML) like..
& on FindButton_Click
this will alternate option of pressing Ctrl+F to find any string on Web Browser..
Now this code works fine for IE6 & IE7.
But if I have IE8 then "find window" is unable to find anything..
Now, if i wrote
WebBrowser1.DocumentText = strHTML
in Page_Load after writing my strHTML to WebBrowser, it worked for me..
I think the problem was that IE8 cant find where it has to find, since navigate URL is "about:blank" So, we have to specify "DocumentText" property..
But this is my guess only, if anybody know the exact reason plz post ur reply