you need to have Win NT or 2000 or linux (kernel compiled for multiprocessing, a good dual processor motherboard and two or more processors which must be of same speed and stepping. thats it.
right now there is no multiprocessing AMD platform (if you wait for a while you mightlay your hands on AMD 760MP for two or more Athlon processors), but you can get dual processor boards pretty cheap these days, those come without scsi like Asus CUV4X-D or MSI 694D (both VIA VT82694 chipset) or Asus CUR-DLS (ServerWorks LE chipset with onboard LAN and SCSI) or Supermicro P6DBE (BX chipset, Slot 1, 100 MHz FSB) or 370DLE (ServerWorks LE chipset without onboard SCSI with socket370 and 133 MHz FSB)
take your pick.
rest is, as jesse says, no different from single processor stuff. even the chassis looks the same.
girish
<font color=blue>die-hard fans don't have heat-sinks!</font color=blue>