Microsoft is pretty clear:
WMF 4.0 can only be installed on the following operating systems.
Windows 7 with Service Pack 1
Windows Server 2008 R2 with Service Pack 1
Windows Server 2012
**You cannot install this software on computers that are running Windows 8.**
Can't even install it on Windows 8.0, let alone Vista. So, your clients on Vista are stuck with WFM 3.0 and PowerShell v3, at most. I've found the use of PowerShell remoting and PowerShell 2 or 3 has been sufficient to manage our pre-7/2008 R2 machines, which is a good thing, because that's as good as it gets for those older operating systems, and as good as it's likely to ever get. WMF 4 support will likely never come to Vista and Server 2008, and will certainly never come to XP or 2003.