TEMPEST protection

Ladies and Gentlemen, I would like to find out how hard (and expensive) would it be to try to protect my computer by TEMPEST-like measures. I am not an electrical engineer and am looking (hopefully) for a relatively easy to understand do-it-yourself type of manual. I have heard from my acquaintaince who is a tempest professional that it was not very possible. If that is indeed true, are there any measures that can be taken to at least complicate spying on my computer? Not that I think that Martians from the flying saucers are already listening, but it is interesting to find out how to do this stuff. Thank you very much. - Igor.