FireFly is alright for rendering... true, it does use a lot more memory than other renderers but the reality is that with a lot of textures loaded into your scene you may well be bumping into a memory issue even with 512mb. I was having a bit of trouble with my other system at 512mb, but with my new box and 1gb of RAM the black renders have disappeared. Should you need 1gb of RAM to render in FireFly? No. Will it require that much sometimes? Yes. It's lame, but the alternative is to export all of your scene objects to something else and take your chances... The extra RAM will probably be a lot cheaper than your time trying to get around FireFly's memory appetite.