I could not find a good PowerShell script which queried the server to see if it was online, then send a WMI query to enumerate the Local Administrators.
Here is a copy of the script I put together
In order to use this script you will need to put together a text file which has all the servers/workstations you want to query. I used DSQUERY to make this text file but you can use numerous tools.
The text file must have the hostname of each member server on a separate line like:
Under the Out-File section, specify the location of where you want the data to be stored.