Upgrading Dual Processor MB over the time.

Planning to build a system for HDV editing. I just wonder would it be a wise idea to buy a MOBO like "Thunder K8W (S2885)" (or anyother one that can take dual core Opteron dual processors) with one processor and add the other processor later.

Will the same logic apply to four processor MBs also- I mean, buying a four processor MB with one dual core processor and adding the other processors over the time.

Will this be economical and technically without any hiccups?

Thanks

Vijjy