I'd run auto-iso, with the limit set at 6400, unless you're wanting to make serious prints from these. Then maybe 3200.
Ditch the tripod. You have the best low-light iso ability on the planet, take advantage of it. If you really want the tripod, you're welcome to use my D200, I'll take the D700 off your hands...
The recommendation to use slow sync flash is a good one, but if you're not familiar with the
look of such shots, I'd mess around with those settings a bit beforehand to get an feel for how it works. Also be aware that the color of the flash on your D700 is unlikely to match the color of the light in the venue, so you can end up with some funky colors that way. Some people like or at least don't mind that effect though.
I'd also suggest using the 50 as opposed to the 24-120, IF, and only IF, it allows you to get decently framed shots. The image quality off that lens is just hands down better, even before you account for the lower ISO values you'll need due to it's large aperture. But it's worthless if you can't get a decent composition with it.
On that same note, do you have a chance to case the joint before you actually go shoot there? If so, spending 20 minutes there with an assistant (any warm body will do), messing with ISO settings, trying the different lenses from the spot you'll actually be shooting from, using the different auto-focus settings, etc, is extremely helpful. Ask any good wedding photographer... chances are they'd never dream of shooting at a location without scouting it out first, even with hundreds and of events and untold millions of exposures under their belts.
Let me build on that idea. One of the things that it took me FAR too long to figure out is that, in digital photography, your own tests, even very simple ones, are worth their weight in gold (ok, they don't weigh much but you know what I mean). You spent all this money on a camera and lenses, so take a half hour to point the camera at something detailed, and try the different lenses at their different apertures and focal lengths. Try all your different ISOs. Experiment with over- and under-exposing your RAW files. See what these things mean to you within the parameters of your own workflow and photographic needs. For any question you might have, the first thing you should do is try to design a test you can do to answer it yourself.
If some guy in a forum says "it's better to underexpose the D700 by one stop and raise the exposure in post", how do you know? Maybe that's just because of his particular favorite RAW software. Maybe he's looking at saturation instead of noise, because he doesn't care as much about noise. Maybe he simply doesn't know what the hell he's talking about. But if you make the two exposures, processes them in the way you'd normally process a shot, and then just look at them... you won't be wondering anymore, you'll just KNOW. All the fear, uncertainty and doubt simply flies out the window once you've figured these things out first hand, and with digital, it's simply not that hard to do so*.
*(Sorry if any of this sounds harsh or critical, it's not meant to be. I find myself running tests all the time that I had the
ability to run the day I got my camera (early '06), and would have saved thousands of exposures if I'd just thought to do them. As they say, it's best to learn from mistakes-- someone else's mistakes if possible!)
