Hi,
you need to use a function JS like
function preview(myContent) {
//open a window, escape special chars
window.open('test.php?myContent=' + escape(myContent));
return false; // so the form isn't submited
}
and the button will look like:
<INPUT type='submit' value='Preview' onclick="return preview(this.form.myContent.value)">
didn't test it but should work.