popup window

Question

I use asp.net
I want to creat popup window when the user type the url
of my main page of the web site
how can I make this popup window to open with the main page

The only that I can do I mae link when user type it the popup open

this my code

<

a href="javascript:void(0)" onclick="window.open('Default2.aspx', 'imagePop','width=380,height=560,resizable=yes,left=500,top=100,status=0')"> Open a new window</a>