I have Windows 2008 on VirtualBox on Linux 2.6 on Athlon II X4 630 processor. When installing Windows the number of CPUs was set to 1 (I forgot to change it). Now I want Windows to use 2 processors (cores), so I changed the setting in VB, in Windows Device Manager I see two processors, but Windows Task manager shows performance graph for only one CPU (and I cannot change processor affinity for applications). So how do I upgrade from uniprocessor to multiprocessor? I found this document on MS site, but Windows doesn't find any other computer types besides "Advanced Configuration and Power Interface (ACPI) PC".
Try setting the number of cores in MSconfig>boot>advanced options. You have to reboot the 2008 VM after doing this.