A few answers to your questions:
(1) For now,Vulnerability Manager will only install and run on a 32-bit OS, which is Windows Server 2003. The next version of Vulnerability Manager will support a 64-bit OS and Windows Server 2008 R2.
(2) And yes, there is a tool to harden the O/S for software only solutions.
Is there a chance that policy adutor and rememdiation manager (software) will have a future version supporting ePO 4.5/Agent 4.5, windows 2008 r2 and windows 7?
When is next version of MVM expected? I couldnt find them in beta section. the current version is 6.8
If not, will McAfee offer trade-in option for appliance?
Policy Auditor 5.2 already supports ePO 4.5 and McAfee Agent 4.5. And is supported on Windows Server 2008. There is a hotfix for PA which allows it to have its client on a Windows 7 system. The current released version of MVM is 6.8, while the next version of MVM will run on the current appliances as well as future appliances. As for a trade-in option, I would suggest that you speak with your local sales rep. :-)
Hope this helps.