object.FreeSpace 

function ShowFreeSpace(drvPath)
{
   var fso, d, s;
   fso = new ActiveXObject("Scripting.FileSystemObject");
   d = fso.GetDrive(fso.GetDriveName(drvPath));
   s = "Drive " + drvPath.toUpperCase( ) + " - ";
   s += d.VolumeName + "<br>";
   s += "Free Space: " + d.FreeSpace/1024 + " Kbytes";
   return(s);
}

Function ShowFreeSpace(drvPath)
   Dim fso, d, s
   Set fso = CreateObject("Scripting.FileSystemObject")
   Set d = fso.GetDrive(fso.GetDriveName(drvPath))
   s = "Drive " & UCase(drvPath) & " - " 
   s = s & d.VolumeName   & "<BR>"
   s = s & "Free Space: " & FormatNumber(d.FreeSpace/1024, 0) 
   s = s & " Kbytes"
   ShowFreeSpace = s
End Function