Function MemberOf() {
    param(
        [Parameter(Mandatory=$false)]
        [switch]$Builtin=$false,
        [Parameter(Mandatory=$true)]
        [string]$Group
    )
    If ( $Builtin ) {
        Switch ( $Group ) {
            ("Administrator" -or "Administrators")
                { $Group = [System.Security.Principal.WindowsBuiltInRole]::Administrator; break }
            ("Backup Operator" -or "Backup Operators" -or "BackupOperator" -or "BackupOperators")
                { $Group = [System.Security.Principal.WindowsBuiltInRole]::BackupOperator; break }
            ("System Operator" -or "System Operators" -or "SystemOperator" -or "SystemOperators")
                { $Group = [System.Security.Principal.WindowsBuiltInRole]::SystemOperator; break }
            ("Account Operator" -or "Account Operators" -or "AccountOperator" -or "AccountOperators")
                { $Group = [System.Security.Principal.WindowsBuiltInRole]::AccountOperator; break }
            ("Print Operator" -or "Print Operators" -or "PrintOperator" -or "PrintOperators")
                { $Group = [System.Security.Principal.WindowsBuiltInRole]::PrintOperator; break }
            ("Replicator" -or "Replicators")
                { $Group = [System.Security.Principal.WindowsBuiltInRole]::Replicator; break }
            ("Power User" -or "Power Users" -or "PowerUser" -or "PowerUsers")
                { $Group = [System.Security.Principal.WindowsBuiltInRole]::PowerUser; break }
            ("User" -or "Users")
                { $Group = [System.Security.Principal.WindowsBuiltInRole]::User; break }
            ("Guest" -or "Guests")
                { $Group = [System.Security.Principal.WindowsBuiltInRole]::Guest; break }
            default {;break}
        }
    }
    ([Security.Principal.WindowsPrincipal][System.Security.Principal.WindowsIdentity]::GetCurrent()).IsInRole($Group)
}

MemberOf -Group "administrators"