Here is a fully functioning script to do it:
Code:
$fdInputFile=FreeFileHandle()
$sFilePath=".\demo.txt"
 
If Open($fdInputFile,$sFilePath)
	"Cannot open file for input"
	Exit @ERROR
EndIf
 
$sIn=ReadLine($fdInputFile)
While Not @ERROR
	$iLineCount=$iLineCount+1
	$sOut=$sOut+',"'+$sIn+'"'
	If Not ($iLineCount mod 5) SubStr($sOut,2)+@CRLF $sOut="" EndIf
	$sIn=ReadLine($fdInputFile)
Loop
 
If $sOut <> "" SubStr($sOut,2)+@CRLF $sOut="" EndIf