I used to run an AMD Duron 1200 'Morgan' on a KT266A platform. By default the C1-Halt State was disabled on this system but using software tools you can enable this. I remember that idle temperatures (using quiet fans that react on temperature) went down from about 60C to ~28C (and power consumption of the CPU accordingly). Tools like CPUIdle Pro can help enable halt-states although I used a different freeware tool back then but I can't remember it's name.
If you have CPU's like 0.13nm Athlon XP-M or the golden era of budget Athlon XP Thoroughbred's (around 8th to 11th week from 2003, especially the 0308MPMW's to 0311XPMW's) you can often run at low voltages if your voltage regulator supports it. If memory serves me well I could run my XP1700+ at 1.1V at default 1466MHz clock on a SiS745 based ECS K7S6A.
thandor.net - hardware
And the rest of us would be carousing the aisles, stuffing baloney.