the worst PC ive got at the moment is an old Pentium I running at a blistering 133Mhz, 16Mb RAM and a 2Gb HDD..... no ports whatsoever apart from PS/2 and graphics, not even sound..... Needless to say i dont even bother switching that one on.
The worst one that i actually use is my beauty of a K6 system, 500Mhz, 96Mb RAM, its a beauty because it has a custom paint job, w00t, UT2003 themed, rocks a$$ severely......