i dont know about the nForce's. are you referring to the nForce2 possibly??? I was only looking at it for Intel Xeon-based servers and it seemed it was built into the new memory controller (E7500 Memory Controller Hub) they were testing out. But Intel says its only 'validated' for ddr200mhz. even if you put ddr266 in it, it will only work at ddr200 speeds.
and as for the memory, its 128-bit ddr. i think i read you also have to do them in pairs too....but dont quote me on that part