Hi,
If you already has a file, you can use this to create a Stream object :
using System.IO;
Stream s=new FileStream(filepath,FileMode.Open,FileAccess.Read,FileShare.Read);
For advanced usage, you can check the (in the downloaded zip file)
Ajax-Uploader\AdvancedCS20-MicrosoftAjax\EditTopic.aspx
Regards,
Terry