Advances in computing saw the introduction of 64-bit x86-compatible CPUs from AMD in the spring of 2003. Intel’s EM64T extensions for x86, which largely mirror the advances made by AMD, have further increased the availability of commodity x86-64 hardware.
Ubuntu fully supports AMD64 processors, and you are encouraged to use the 64-bit version of Ubuntu to get the maximum from these advanced processors.
As far as the Intel Itanium architecture goes, unfortunately Ubuntu does not currently support ia64. However, you might want to investigate Debian, which is available for the ia64 platform and several others.