More on Dual CPU motherboards

Hi all, Like Mr Alderson, I'm looking to start building a box. I'd like it to be multi-processor, but really can't afford to buy 2 CPU's at one time. So, can a dual processor motherboard be run with only one processor installed? I figure this is likely to be a jumper setting or bios option? I also assume both the processors have to be identical - am I right in that? or could I add a faster version of the same type as the first? I figure that the second would then have to run at the same speed as the slower unit in that case, but subsequently a third can be swapped in to replace the slower one. Thanks Dylan -- Sweet moderation Heart of this nation Desert us not We are between the wars - Billy Bragg