I have Vista 64bit SP1 machine. But I did not run into what you reported here.
BTW, I'd like to clarify that iisprovider.dll file, which is the IIS Powershell provider dll, is not copied to the PowershellProvider directory. It should be copied to GAC like this.
C:\>dir C:\windows\iisprovider*.dll /s
Volume in drive D is New Volume
Volume Serial Number is 40B7-51EA
Directory of C:\windows\assembly\GAC_MSIL\IIsProvider\7.1.0.0__1a5b963c6f0fbeab
04/14/2008 10:50 AM 136,216 iisprovider.dll
1 File(s) 136,216 bytes
BTW, as you might know, in 64bit OS, there are two version of Powershell. Did you use %windir%\SysWoW64\WindowsPowerShell\v1.0\powershell.exe?
If so, you should use %windir%\System32\WindowsPowerShell\v1.0\powershell.exe. This is a known product issue in this Tech Preview 1 build.
Please let me know if this is your case.