The fact that anyone would consider buying a 400Mhz computer with a 6G HD and 384Mb RAM, for any price, is scary. Additionally, without an installed operating system, you'd better be pretty savvy with computers before attempting to load one. I guarantee that you'll spend your $80 and you'll never get it to work.
Dell is offering it's Dimension 3000 P4, with 2.8Ghz CPU, 40Gb drive, monitor, XP, DVD, 512 MB SDRAM, etc. for $529. The SDRAM alone is runnnig at 400Mhz, or as fast as that $80 machine of yours. Don't buy it...