I need boot any images from iSCSI and I'd like to boot from linux console of a previous LiveCD booted. Is possible, without gpxe, ipxe firmware or similar? With a simple iSCSI initiator for example?
Whether you can or cannot boot from iSCSI depends on whether you are using a hardware iSCSI initiator or using the open-iscsi initiator on a system with firmware boot support for iSCSI (such as iSCSI Boot Firmware, etc.).
Look at the Red Hat 5 or 6 documentation for more information regarding iSCSI initiators.