40 megs? You might have server restrictions to deal with.
Actually, Activex for IE folks and XMLhttprequest for the others. It's called Ajax. I think it could handle what you want. In this case, it could be a cross between php and javascript.
http://www.adaptivepath.com/publications/essays/archives/000385.php
Do a further search on Ajax and you'll find resources. I've used it for a number of things and it's really pretty simple to work with.