Ubuntu doesn't have to see 4 cores for the cpu to work. Only the motherboard has to have support for your cpu. Ubuntu is an imperfect software; if you want more toys and support, go with windows ultimate. It works great, especially with a directx 10 or 11 video card.
Actually, it was the BIOS - I went through it and enabled "ACPI" and (?) "EACPI" and now I see 4 cores as I'd hoped.