I don't know specifically if SME has any problems on a 64bit machine, but if it will run on a 32bit machine it will run on a 64, it just won't use it's capabilities.
If it will support the hardware (nic, video... whatever) it will work.
I have two in the office running XPPro (not the 64 bit edition) and all is well. No drivers available for all but one of the printers in the office for the 64 bit edition.
You're thinking to hard about what a 64 bit computer is...
286 - single lane road
386 - 2 lane road
486 - divided highway
586 - 4 lane freeway
686 - 8 lane super highway
You get the idea - still just roads. 64 bit - really big road, but still a road.