I have used:
$ComputerlistPath = 'c:\temp\computerlist.txt'
$ComputerList = Get-Content -Path $ComputerlistPath; # one computer a line
foreach ($computer in $computerList){
($computer + ": " + @(Get-WmiObject -ComputerName $computer -Namespace root\cimv2 -Class Win32_ComputerSystem)[0].UserName);
}
To get this information a few times. you can probably use this as a basis to make a script do what you want.