To install, first open ArcToolbox in either ArcMap or ArcCatalog. Right-click in ArcToolbox and select "Add Toolbox...". Navigate to the folder where you un-zipped the download, select the .tbx file, and click the Open button.
To edit the script, open the toolbox you just added, right-click the tool and select "Edit".
"Running script ASCFileToXYZFile...
<type 'exceptions.ImportError'>: No module named os
Failed to execute (ASCFileToXYZFile).
End Time: Tue May 08 00:41:06 2012 (Elapsed Time: 0.00 seconds)"