Yes, you can put JavaScript anywhere in an HTML document (or ASP, or PHP, etc.), although to have a valid page you would put it within the <html> tags.
Chris' function should work, but it doesn't always actually maximize the window. It just makes it span the width and height of the screen. Usually the maximize button will still be maximize, not minimize. But if it's close enough that you don't care, fine with me.
This code opens an absolutely fullscreen window:
<script type=text/javascript language=javascript>
var nw = window.open('yourpage.asp','nw','fullscreen');
</script>
Notice that I did specify the language and script of the <script> tag, although it is not usually necessary with JavaScript. I believe there's a <meta> tag that allows you to define the default scripting language.
HTH,
Snib
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