Hi Ron,
I don’t recall using an SFTP adapter from a BizTalk orchestration to exchange information with external partners, but I implemented a standalone .NET application which transferred a data file to an external partner using SFTP protocol, and this program resides in our secure corporate internal network (behind a firewall). So I assume that you could do the same for your BizTalk scenario.
Also, BizTalk 2006 R2 platform does not supply any SFTP adapter with its SDK, so you will need to buy a third-party software module to implement that in your project. One good place to look for that kind of adapter is /n Software Inc., and here is the link to that particular adapter:
http://www.nsoftware.com/products/biztalk/adapters/sftp.aspx
Best of luck with your project!
Daniel.