I started with a sysprep vpc Windows 2003 SP1. After setting it up through VPC console I started with patching and SP2 (this may take a while, depending on your host system). Next step is installing some prerequisites like IIS 6.0, Office Excel/InfoPath 2003 SP2, Visual Studio 2005, SharePoint Services 2.0, SQL Server 2005 SP1. This needs to be done to use HTTP, SOAP Adapter, WSS Adapter, SSL encryption and for BAS en HWS (last two I am not really interested in, so I left out InfoPath as well, which one needs for BAS configuration and use as BAS client). Doing installing all prerequites is quite a long ride behind a laptop doing it on VPC 2007, it helps having full access to them through an MSDN subscription. Learning aspect here is that one gets a good view what it takes to bring up BizTalk Server 2006 R2. I must say having a good installation guide that the Microsoft people made helps a lot too (especially explanation why some prerequites are necessary together with some background provided makes things more understandable). Another useful tip I can give you as a reader with the same desire to complete rollout a BizTalk Server 2006 R2 on VPC 2007 is using poweriso or daemon tools inside your virtual machine and mount images on your local (host OS) drive or preferably external hard disk. Oke through to next phase installation of BizTalk Server 2006 R2 itself, finally the main event. Installation went smoothly and it started off with downloading .cab file with prerequites like .Net 3.0 framework, SQLXML 3.0 SP3, ADOMD.NET 9.0 (comparable installation flow like current BizTalk 2006 version). Then it installs all things I checked (see picture below).
Finally configuration of BizTalk Server where installation guide opts for basic, I usually choose custom so I can do configuration step by step. I configured almost everything see picture below.
This finishes installation/configuration of BizTalk 2006 R2 Beta 2. Next stop taking it for a spin (try a couple of things out). Installation/configuration guide can be downloaded from Microsoft. Same accounts for the BizTalk Server 2006 R2 (you will have to apply for it).