with only 128 of ram I'd recommend installed Win 98 instead of xp. I can't really say which version of mame is best for you, but I had an 800mhz machine with XP installed (but 3x as much ram as you) and I had problems running games like bubble bobble 2 or puzzle bobble 2,3,4. It could run them, it just stuttered a quite a bit at times. I was able to play all versions of metal slug and king of fighters without problems though.