How to run a PowerShell script within a Windows batch file

It sounds like you're looking for what is sometimes called a "polyglot script". For CMD -> PowerShell,

@@:: This prolog allows a PowerShell script to be embedded in a .CMD file.
@@:: Any non-PowerShell content must be preceeded by "@@"
@@setlocal
@@set POWERSHELL_BAT_ARGS=%*
@@if defined POWERSHELL_BAT_ARGS set POWERSHELL_BAT_ARGS=%POWERSHELL_BAT_ARGS:"=\"%
@@PowerShell -Command Invoke-Expression $('$args=@(^&{$args} %POWERSHELL_BAT_ARGS%);'+[String]::Join([char]10,$((Get-Content '%~f0') -notmatch '^^@@'))) & goto :EOF

If you don't need to support quoted arguments, you can even make it a one-liner:

@PowerShell -Command Invoke-Expression $('$args=@(^&{$args} %*);'+[String]::Join([char]10,(Get-Content '%~f0') -notmatch '^^@PowerShell.*EOF$')) & goto :EOF

Taken from http://blogs.msdn.com/jaybaz_ms/archive/2007/04/26/powershell-polyglot.aspx. That was PowerShell v1; it may be simpler in v2, but I haven't looked.

This one only passes the right lines to PowerShell:

dosps2.cmd:

@findstr/v "^@f.*&" "%~f0"|powershell -&goto:eof
Write-Output "Hello World" 
Write-Output "Hello some@com & again" 

The regular expression excludes the lines starting with @f and including an & and passes everything else to PowerShell.

C:\tmp>dosps2
Hello World
Hello some@com & again