Using Poweshell Add-Computer on Script startup

Question

Is it possible to user Add-Computer in a Startup script in windows2008r2? 
The script works after the computer has been boot, however when we added into the startup script it fails. 
Any other way to do this on startup 

Answer 1

Let me explain a little bit more the question, I know I wasn't clear. 
I have a EC2 AMI (Amazon Image) which has things preinstalled. Windows instances are created using the image. 
As part of the image we have some startup script that perform tasks given the instance. As part of this initial setup we want the instance "auto" register to the AD server. 
Using a powershell script we able to detect whether the instance is part of the domain, if not we added to the domain using Add-Computer. This means that only when the instance is created the script will register to AD, otherwise it will ignore the command. 
A snipped of the script is:
if ((gwmi win32_computersystem).partofdomain -eq $true) {
        //DO other things since it is already joined
      }else{
        $username = 'user';
        $domain = 'domain.com';
        $password = 'pass';
        $credential = (New-Object System.Management.Automation.PSCredential ($username, (ConvertTo-SecureString $password -AsPlainText -Force)))
        add-computer -domain $domain -credential $credential -OUPath '#{node["ad"]["ou_string"]}' 
The script is not the issue. The question is when/where to run the script on startup? 
Any suggestions?