With my D700 and the Sigma 2.8 70/200 (oldest version) the D700 locks up when i change anything to do with autofocusing. As long as i keep everything the same there is no problem. Non of my other lenses have the same effect.
I have the older version (without DG) i do not know if the newer versions are anny better in combination with the D700. With my D200 the lens worked perfectly.If I may, is this the Sigma glass you're talking about: Sigma 70-200MM f/2.8 APO EX DG HSM AF?