You don't need to strip the CRLF - it's implied by ReadLine(), but is not actually present.

This sort of loop will catenate 5 lines:
Code:

$sIn=ReadLine($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