Actually, the ia-64 version is for the Itanium. For Athlon 64/Opteron, you would want the amd64 version. I'm not sure how far Debian has gone along on the amd64 port - it looks like they have a lot of things working, but aren't ready for prime time. You can check the Debian-amd64 mailing list at
http://lists.debian.org/debian-amd64/ . There's also an official page at
http://www.debian.org/ports/amd64/ . With the amd64 port, you should be able to run 64-bit and 32-bit binaries side-by-side.