advice on using rental lenses for D700
Yes, they're heavy and demand some discipline in handling them.
First--go to Photozone.de to look at the resolution figures for both lenses and shoot at optimum apertures, e.g. through about f/8, in order to keep diffraction from being a problem. Even at that, you probably won't see much of a loss of detail on the D700, if you go past f/8. I've been shooting those lenses with my D700 for about three years and they're very good.
Second- use your tripod for best resolution. They both can be hand-held, but not for very long. The 24-70 doesn't have VR, so you need shoot at lower f-stops or push the ISO up to get something > 1/125th of a second, if you plan to go hand-held. I've gotten good results with ISOs up to 3200 and a little bit of noise at 6400.
The 70-200 VRII is a great lens, is heavy, but the VR will support being used handheld. If you mount it on a tripod, be sure to turn the VR off on the lens barrel. You might want to rent a TC-14 or TC-17, if you plan on shooting things farther away. Then, a tripod is absolutely necessary, due to the loss of 1 or nearly 2 stops.
Autofocus with both lenses is very fast and accurate.