If you use JavaScript, or a JavaApplet, you should be able to do this. I found this on the web:
Function form1_onSubmit ()
Set WSHShell = CreateObject("WScript.Shell")
Set fso = CreateObject("Scripting.FileSystemObject")
Set file = fso.GetFile(document.form1.file.value)
filename = file.size
if (file.size > 6291456) then
MsgBox("The File is too big to upload")
form1_onSubmit = False
else
form1_onSubmit = True
end if
End Function
Here is the link to the actual thread:
http://www.experts-exchange.com/Web/Web_Languages/JavaScript/Q_20765620.html