Q: Can I run BizTalk Server 2006 R2 on Windows Server 2008?
Q: Can I (should I) run BizTalk Server 2006 R2 on Windows Server 2008?
A: No. And these are the main resources I give customers who wants to see some kind of Microsoft reference to this:
Q: Can I (is it technically possible to) run BizTalk Server 2006 R2 on Windows Server 2008?
A: As I mention (but perhaps do not emphasis) in the answer to the first question of this post "Can I (should I)" is an answer directed at customers. From an technical aspect it is possible to install and run at least the main parts of BizTalk Server 2006 R2 on Windows Server 2008 (see this post), however it is not supported. As such the answers to customers is (so far) still no. But then again up until quite recently it wasn't really supported to run BizTalk Server virtualized on VMWare either (but now it is) and we still did that so maybe I'm being over-cautious? It's not the same kind or level of support we are talking about though...
Q: Can I (should I) run Windows Server 2008 as the host OS on which I run virtualized guest OS with BizTalk Server 2006 R2 though Hyper-V?
A: Yes. As long as the guest OS is compatible with BizTalk Server 2006. Ie Windows Server 2003 (, XP or Vista). See the BizTalk Server 2006 R2 Hyper-V Guide.
UPDATE: I updated this post after comments. Thanks Jocke, it's certainly more complete now.