Internally ASP.NET has a 2 GB addressing space, but in reality you only have less than 1 GB free for uploads (see http://support.microsoft.com/?id=295626 ). In addition IIS
I actually did the exact same thing recently. I created a Silverlight Client app to handle chopping up the data and sending it to Azure.
This is a working example that I followed that does exactly that. Pretty much follow this and you're work is almost much done for you.