You can use following javascript code to dynamically adjust width and height of the page viewer webpart.
Just put it in each asp.net page that you want to display in a page viewer, and the problem will be solved:
Javascript code:
function resizeMe(that) {
window.resizeTo(document.body.scrollWidth, document.body.scrollHeight);
}
window.attachEvent("onload", function() {
window.setTimeout("resizeMe()", 100);
});
Alternatively, window.resizeTo(window.screen.availWidth, window.screen.availHeight); can also be used.