When booting a Compaq Proliant 5400 (4x200MHz PPro) off a "install-x86-universal-2004.0.iso" created CD, and choosing "smp" as the kernel, I get the error "8254 Timer not connected to IO-APIC" and the boot process halts. With the plain "gentoo" kernel, all is well... Googling the 'net turns up quite a few links, but the "solutions" provided do not seem to be of much help here (e.g. recompile you kernel). BTW: RedHat Enterprise 3 also fails (just hangs, no error message whatsoever) if one tries booting the smp kernel - single processor kernel boots/runs OK.
looks like a kernel bug if redhat does not work either. contact the kernel devs