Some socket 478 celerons - those things sucked big time. A friend of mine had a 2.2Ghz cellery with 128kb of cache that felt a lot slower then my (then) XP 1800+. It was also a pain in the neck trying to get one of those setups to run decently when I had to install windows on one. To make it worse, they usually used low budget mainboards as well - the worst of witch had no AGP slot, shitty CPU power circuitry, limited expansion options and so on.
There's also some wierd PCChips boards with a soldered CPU - some were based on the AMD Duron - usually 800 or 1200mhz parts, others on the socket 370 celeron - this in 2002-2003! SDRAM, no AGP slot.... I had to install winXP on those things...
K6 / Pentium II / slow Pentium III rigs with 256mb of ram running windows XP in 2001-2002 - I saw a lot of these back in the day. They came into the shop I worked at part time and people insisted on installing XP on them. Some listned to reason and went with 98 or upgraded to a faster machine, while others continued with their madness. I remember it took for ever to install XP on one of those...
Budget laptops... modern machines you can pick up for 200$ - they come with some shitty pentium / celeron dual-core, clocked at a "speedy" 1.8ghz, or some dual core AMD APU. 2Gb of DDR3, some soldered with no expansion slots, some with one populated expansion slot - single channel 64 bit only (and trust me, dual channel can make a big difference in older machines, especially ones with on board video), 5400rpm hdd, poor quality lo res screen with a glossy finish you can see your face in and horrible washed out colors - god I hate these things - and a lot of people buy them in my country - A LOT!