I use these two functions to quickly setup Powershell to execute Ruby code under either MRI or IronRuby easily. Simply add them to your Powershell profile.

function set-ironruby() {
$env:path = ";c:\ironruby\bin;c:\ironruby\lib\ironruby\gems\1.8\bin;" + $env:path
}

function set-ruby() {
$env:path = ";c:\ruby\bin;" + $env:path
}

Then you can use it like so..

rubypsfunctions