Build a cheap computer

Recipe for a US$150 build.
The computer has just five components (mobo, HD, RAM, CDROM and case) with only the mobo and HD being $45 or more.
Of course, you'll notice there's no monitor, mouse or keyboard which may prove troublesome for newbies.
Additionally, only free software is used to get it working which of course is so much better.
One problem for me, of course, is that being in Ireland, the 150 price would probably increase three times, as well as being in euros, so the actual price would probably be about 5 times what's mentioned in this article.