opening url in new browser...but url is along a different directory structure

I have some code I can use to open a url in a different browser window

Response.Write("<SCRIPT language=javascript>var w=window.open('Report.aspx');</SCRIPT>");

But the aspx "report.aspx" is actually along a different directory path. Its a couple of levels lower and one level up the tree.

('~/Utils/Reports/Report.aspx');

but using that structure doesnt work in teh above example.

So anyone knwo HOw I can open the url with the diferent path like in teh above example.

I cant put in a static http: url because it changes depending on teh enviornment the app is installed in.