Based on a thread today on the MSDN forums I tried working with BizTalk 2010 RTM and the Commerce Server 2007 adapters. These are the same adapters used for Commerce Server 2009. I had worked with these adapters on a recent project with BizTalk 2009. I just wanted to post that the adapter install went successfully and I was able to add the adapters in the BizTalk 2010 administration console and able to create ports like normal. So this is an excellent compatibility story.
I had already confirmed these adapters worked with W2K8 R2 about a year ago. My test today of BizTalk 2010 RTM was also on W2K8 R2 with SQL 2K8 R1. Be aware that I only tested the BizTalk adapters and did not work with the Commerce Server business applications or any other aspect of Commerce Server.
Last year Cactus eventually certified/verified that these same adapters appeared to work successfully with BizTalk 2009: http://blogs.msdn.com/b/rdonovan/archive/2009/07/22/biztalk-server-2009-now-works-with-commerce-server.aspx, so I would expect a similar announcement eventually.