Perhaps the FileSystem Object would help out here, you can read 1 line at a time with that. Although like Les said, this will open the entire file in memory too but I like to think FSO handles files quicker then Kix does.

 Code:
Dim $Script, $FSO, $ReadScript
$Script = "C:\boot.ini"
$FSO = CreateObject("Scripting.FileSystemObject")
$ReadScript = $FSO.OpenTextFile($Script, 1)
While Not $ReadScript.AtEndOfLine
  ? $ReadScript.ReadLine
Loop
$ReadScript.Close
$FSO = ""