I'm sure there's some way to do a for loop in dos, or you could always install cygwin and do:
for i in *mp3; do lame -whatever "$i" "${i}.mp3"; done
.. or install python and do:
import glob, os
for i in glob.glob("*mp3"): os.system('lame -whatever "%s" "%s.mp3"' % (i,i))