first off this is a older system circa mid 2007 as such intel has no plans to release updated microcode for cpu's of this generation. and system venders no longer provide any support for systems this old.
next, hp has on several ocasions release updated cpu microcode to support newer cpu's on systems this microde only updates the cpu support in most cases and as such simply adds the new microcode to the existing bios
if at a later date hp then releases a newer bios for that system that fixes/adds enhcancments to the system via the newer bios, if will by default include the previous microde updates released previously
to recap:
there is no need to install the microcode update and then a newer bios update, since the newer bios by default will allready have the latest microcode