i always used this, to get a div in 100% height:
[Head]
<style type="text/css">
html, body{height:100%;}
</style>
...
[Body]
<body style="margin: 0;">
...
And then add a style to the div, table, or something else with property width and height at 100%...
but with internet explorer 8, this isn´t enough... then i foud this:
[Head]
<style type="text/css">
html {height:100%; width:100% }
</style>
[Body]
<body style="margin: 0px; height: 100%; width: 100%; padding: 0px">
<form id="form1" runat="server" style="height: 100%; width: 100%;">
Now, you just need to add the same tag, the style property height set to 100%
hope it helps :D
credits: http://forums.asp.net/t/1445134.aspx