It doesn't mean much of anything. The A64 has an on chip memory controller and has a hypertransport bus to the chipset. Thus, a lot of the marketing BS says that it doesn't really have a front side bus. However, in the most basic of respects, the FSB works similar to all other systems.
As far as buying a CPU, I don't know what you mean. In the AMD world, pretty much if the CPU has the same number of pins as the socket, it will work.