Box.net, the online file storage service that offers 1GB of free storage space, has developed some excellent add-ons that could make this service a darling for Microsoft Office users.Box.net offers a virtual file explorer for your uploaded documents, pictures and videos. You can put this file explorer anywhere in your website and visitors can easily navigate through your files, download them offline or they can subscribe to your files in their newsreader.Today, Box.net unveiled another useful service called "Office on Deman