Not very strong... If I remember right it's all CPU and connection speed, with a little RAM thrown in. Only need enough video to do work on the machine itself, not for game play. A 2-3GHz CPU should be plenty, might have to research and see if dual core will even use the 2nd core. Couple Gig's of RAM just because. This is a game from what 2007, 2008? 12 people shouldn't be much of an issue for that or even less I wouldn't think.
Are you thinking of buying parts for this, piecing one together from spares, or trying something on a virtual machine inside your main rig?