I don't think you can change the size of the Centerweighted Area when using a Non-CPU lens ... ?
(I once read about that in the downloaded manual despite not owning the D700 myself, and I had a post about it in the below mentioned thread).
Please also note my remark about the Spot metering being locked to the center focus point with a Non-CPU lens. It's rather important, and to be honest rather annoying, in my opinion.
See my post # 20 in this thread: http://forum.getdpi.com/forum/showthread.php?t=4328