[Foreigner]

feytan,
Можно еще так. Будет побыстрей:

Код:

@echo off
setlocal enabledelayedexpansion

for /f "tokens=*" %%i in (filelist.txt) do call:1 old "%%~i"
set "n="
for /f "tokens=*" %%i in (renlist.txt) do call:1 new "%%~i"

for /l %%i in (1,1,%n%) do ren !old_%%i! !new_%%i!

goto:eof

:1
set /a n+=1
set "%1_%n%=%2"