The earlier 64 bit processors that didn't support 32 bit were Intel Itaniums, which came out a bit before AMD did their x86-64 extensions for their processors. Then everyone saw 64 bit didn't have to be retarded and the Itanium, its funky workstation/server applications aside, became almost laughable. But its still a decent platform that is still in use, I hear they're even working on a 128 bit version.
tl;dr: 64 bit is backwards compatible, so it'll work.