I have been working with the Sharepoint Adapter from GotDotNet. I have been desperately trying to find a way for BizTalk to get a file from a location and then move it into Sharepoint with retaining the filename. Well if you are looking to do this you cannot. I was looking around HAT and saw that each message has message properties, with information that I could use. Lucky for me that if you are using the File and Sharepoint the way I am InboundTransportType=FILE and ReceivedFileName='the file name'. So you might be asking how you get to them, easy, the msg variable is already defined for you. Using msg, you can access all the message properties by using the following code:
msg.Message.Context.Read("ReceivedFileName", "http://schemas.microsoft.com/BizTalk/2003/file-properties").ToString();