How to handle double entry check java script prompt using selenium

any one help me out, scenario: need to fill the double entry check prompt/alert This prompt/alert has two text boxes.. need to fill these two and click on ok button.

Tried solutions: 1) Switch to the prompt/alert using Alert alert1=driver.switchTo().alert(); with out any error able to switch to alert. but unable to locate textboxes. 2) This prompt looks like window.. but by using getWindowHandles() is not giving any of window code to this prompt.. so it mayn't be a window..

Thanks, sateesh.k