What operating system and update should be installed to have dual-core support in the kernel for the system?

Updated -

Dual-core is not supported in Advanced Server 2.1. It is, however supported in Red Hat Enterprise Linux 3 with update 5 or later as well as Red Hat Enterprise Linux 4 update 1 (NUMA is disabled by default), update 2 (NUMA is re-enabled by default), and higher.