The Psyco docs say:
Just for reference, Psyco does not work on any 64-bit systems at all. This fact is worth being noted again, now that the latest
Psyco assumes that sizeof(int) == sizeof(void*) a bit all over the place. That's much harder than just writing down 64bit calling conventions and assembler. On the sidenote, pypy has 64bit jit support these days.
Cheers, fijal