Ther are various ways to toggle visibility... in Poser 7, the visible tag in the propertie menu is animatable, so you can simply do it from there. You can use the scale trick, by setting a keyframe the frame before you want it to disappear at 100% scale, and then move forward to the next frame and set it to 0% - instant vanishment!

A third way to do it, and the way I tend to prefer, is to use the transparency value in the material room. It's done in a similar fashion to the scale, but you have to toggle the animatable switch (the key by the value) in order to make sure it sets keyframes. 

JonTheCelt