This article is based on the article File Upload from Silverlight using WCF. So please read it before proceeding with this article.A while back I wrote an article on uploading a File from Silverlight to a server location using WCF. I found my own article quiet useful. However, when I reread and implemented the code, I mentioned in the article, I found a few discrepancies:
Consuming ODATA in Silverlight 4.0
Smooth Streaming Over Silverlight
Try this post to upload files more than 5 MB :)