Powershell Add a Login to SQL Server

I have a need to write a script that will check to see if a Windows Group exists on a server instance and if not then add it. I was attempting to do this using Powershell and SMO, but I was not really having any luck with that. I changed modes and I have decided to use the invoke-sqlcmd commandlet to get the task done. I use SMO to determine if the group that I want is on the server. If not then I create it. Like so:

$instance = “server\instance”

[System.Reflection.Assembly]::LoadWithPartialName(’Microsoft.SqlServer.SMO’) | out-null
# Create an SMO connection to the instance
$s = New-Object (’Microsoft.SqlServer.Management.Smo.Server’) $instance
#$s | Get-Member -memberType Property
#$s.logins | Get-Member
$logins = $s.Logins
$query = “CREATE LOGIN [domain\group name] FROM WINDOWS WITH DEFAULT_DATABASE=[master], DEFAULT_LANGUAGE=[us_english]“
$dba = $logins | where{$_.Name -eq “domain\group name”}
if ($dba -eq $null)
{
Echo “DBA Group does not exist.`n Adding Group”
Invoke-Sqlcmd -ServerInstance $instance -Query $query
$logins = $s.Logins
$dba = $logins | where{$_.Name -eq “PNI\PNI SQL SYSTEMS DBAS”}
if ($dba -ne $null)
{
Echo “`n Group Created”
$dba.name
}
}
else
{
Echo “Group already exists.”
$dba.name
}

Not to hard and it is nice to be able to use SMO to check for the login and then Powershell to create it.