SUTABLE MOTHER BOARD AND CPU

Linux can technicaly run on anything from a 386 upwards, all depends on what version you want and what you want to do with it.

If its just to have a muck around and teach yourself, then build a machine from using some cheap 2nd hand parts and stick to intel based chipset/cpu, 3com/realtek/broadcom for network card and an older geforce/ati video card.