My oldest PC is a HP 486 GA/50 with 512 MB HDD and 16 MB RAM, not to forget a 1MB SiS graphics card and2x CD-Rom drive.
I have Pentium 3 desktop machine running at 996 MHz and 128 MB RAM, installed on 82810 Intel motherboard. I'm still using it, but it does become heavy (and slow) when it comes to running today's apps.