You may have to explicitly declare
all of the window features in IE 5.x:
PHP Code:
window.open('some_page.html','popupWin','width=400,height=300,scrollbars=0,menubar=0,directories=0,status=0,toolbar=0,resizable=0');
NOTE: You may want to set scrollbars to 1 unless you're absolutely sure the page content will never be taller than the window height.