APIC is the new IRQ scheme that newer motherboards support. Its been around for about 2 years now. Instead of the old limit of 16 IRQs, APIC allows 200+ IRQs. Which means nothing needs to share an IRQ if the OS supports it.
For MS Windows, only 2000, XP, 2003 and higher support it, and it must be enabled in the bios when the OS is installed. It cant be swiched on afterwards.
It has to be disabled in the bios for 95, 98, and ME, or you get crashes.
Many motherboards coming out now dont have the option to disable it anymore, which might be a problem.
Be best to use it if possible. I'd guess SME 7 would support it, but havent tried.