Tom's Hardware Guide checks out what happens when you mix a dual and a single-core processor in a PC.
For AMD and Intel, it is just a matter of time before single-core processors become a thing of the past. The future thus belongs to devices that might pack two or eventually more than a dozen physical processing units onto a single physical die. However, it is a common assumption that processor cores have to come in even numbers, which is, in fact, not the case.
When we compared a dual-core and a dual-processor system, we first mentioned the possibility that the two might work. IBM's processor for the Xbox 360 is a triple core, which is a pretty good indicator that this configuration is viable. Although the power requirements are clearly different, there is, after all, no difference between single- and dual-core processors.