How do you make an object appear and disapear during an animation?

Depends on how fast the transition between visible/invisible,  and your Vue version.

Getting the objects Material Tranparency setting in sink with the frame rates, as bruno indicates.

Rememebr, if it has to appear and disappear quickly, you need ot key frame it for that, so the transition occurs over two frames (soild  -->inviisble, or the reverse, ) and the initial state of the object at start of animation!! 
this is curucial, Vue it willl assume you want to blend the visibility state between begining of animation, and start of the changes. If this occurs over many frames, it will slowlly appear/disappear.

So, it could be done thus:

Frame 1 = invisible (sets basic state, not seen at all)

Frame  50= invisible (sets LAST frame for this state)
frame 51 =  VIsible (sets first frame for this state)

frame 90 = Visible (last frame for this state)
frame 91 - invisible (first frame for this state)

:)

Why I asked for your Vue version, is because in Infinite, if this has to be done quickly, you can simply keyframe the "hide from render" state, but hide from render is Infinite only. ( and xStream, of course)

Quote - Why I asked for your Vue version, is because in Infinite, if this has to be done quickly, you can simply keyframe the "hide from render" state, but hide from render is Infinite only. ( and xStream, of course)

I have Vue 6 Infinite Pro, and could you go over the steps to do this again please..

Let me try to understand this whole thing, (1) I check on hide from render then set a key frame for x-amount of frames (2) check hide from render at the end of the amount of time that I want it to be hidden (3) uncheck hide  from renderand add a key frame at the start of the new sequence?
This didn't work the object was still visible after I rendered it.
Is hide from render the only way to accomplish this?

No, the other way would be to make 100% transparent all materials for the object, and make them 0% transparent when you want the object to be seen again. Then it depends on what you want if you want a quick change between visibility states, use 2 keyframes between states, or if you want a transition between states, let about 12 seconds between keyframes and say yes when Vue asks you if you want the change of matrials to be animated. Vue will then create a sort of morphing from visible to invisible during the time you left between keyframes. 12 seconds is good for a nice effect.

Quote - No, the other way would be to make 100% transparent all materials for the object, and make them 0% transparent when you want the object to be seen again. Then it depends on what you want if you want a quick change between visibility states, use 2 keyframes between states, or if you want a transition between states, let about 12 seconds between keyframes and say yes when Vue asks you if you want the change of matrials to be animated. Vue will then create a sort of morphing from visible to invisible during the time you left between keyframes. 12 seconds is good for a nice effect.

Ok I will give it a go...