Install the supported OS, BT2009 prerequisites and BizTalk 2009 server itself as described in the BizTalk 2009 installation documents found here.
Install the WCF LOB Adapter SDK SP2 and then BizTalk Adapter Pack 2.0 as described in this blog post.
Afterward, install all the SAP RFC Runtime and other component downloadable from SAP Marketplace. The detail components you need are in installguide.htm of the SAP Adapter Pack downloable here.
Here is a little bit clearer sample instruction on what to do w/ the file downloaded.
If everything went right, Add Generated Item should work properly and so does Add Service Reference on non BizTalk WCF project.
I blogged regarding a particular error that you will received from not entering the correct Action during the WCF-SAP send port configuration in this post. but I didn't tell you what to put in there.
What should be in there is something like: http://Microsoft.LobServices.Sap/2007/03/Types/Rfc/BAPI_NAME_YOU_WANT_TO_CALL. Replace the last part with the appropriate value.
The easiest way I found to do this is by creating a WCF console application to consume an Adapter Reference to SAP and basically pick the BAPIs you are interested in and after it created the sapBinding.cs file, just open it and browse for the BAPI that you wish to map to WCF-SAP port, copy and paste the URI string that will look similar to the one above into the Action textbox of the WCF-SAP port setting.
If anyone know of a better way, please let me know.