All of the x86 flavor 64-bit processors (IA64 and x86_64) will run 32-bit x86 applications. CentOS (RHEL) comes with a complete set of 32-bit libraries.
not to be pedantic or anything, but IA64 refers to Intel Itanium, which isn't really x86 flavor at all, and runs 32bit x86 poorly at best. both AMD's am64 (opteron, athlon 64, etc) and Intel's em64t (core duo, late model Xeon, etc) are considered x86_64 architecture.