It is a bit of a hack, but the following works in Vim 7.2. Notice, I am running Powershell within a CMD session.
if has("win32")
set shell=cmd.exe
set shellcmdflag=/c\ powershell.exe\ -NoLogo\ -NoProfile\ -NonInteractive\ -ExecutionPolicy\ RemoteSigned
set shellpipe=|
set shellredir=>
endif
function! Test()
echo system("dir -name")
endfunction
Tested with the following…
:!dir -name
:call Test()