I said procedural animation, not spiders. Spider-like creatures can be certainly added but they won't move as realistically as in the video old_andy posted. Head over to Martigen's Mutant Mod (basically it's a mod that will adds all kinds of critters to NV) thread and post your suggestion. Keep in mind that Martigen doesn't do mesh work though (at least I think he doesn't). You could ask Sloth for the models since she likes spiders (she created a spider mesh for OB IIRC) but I'm not to sure she mods for NV.
Wouldn't look any less crap than Radscorpions or Giant Ants. Having said that, it's still going to require an extremely talented modeler to make anything even remotely believable.
Ahh okay so Spiders can be added then. Well, I have not a problem if they wont have the exact animation required as long as they work properly in the Fallout World. I think spiders would be a nice addition to New Vegas. So yeah I am going to head over to the MMM thread and post my suggestion there.
The problem is they are going to move in the same crappy way that everything else with more than 2 legs does in Fallout. Every time they encounter a change in elevation or try and walk over any kind of rock or object they are going to clip through the ground and start walking at funny angles, but then that's what the original models do so I don't think adding another one is going to make the game look any worse than it already does.