The game may be playable on a single core processor, depending on its class and speed. Maybe someone who has done so can give some feedback on the performance they got. One of the fixes in the second German patch (included in the English release) was improved performance on single core processors. At least based on the unpatched German release, Pentium 4 CPUs more than 3GHz may do ok, while AMD single cores experienced worse performance (see
here).
