Would i be correct in believing that the perpose of a movie clip symbol is to give the effects which can be gained with multiple frames while actually sticking in just 1 frame and applying it to only one object.
the reason i ask is that i was wondering how you would have a flash based website with links which fade to a new colour on mouseover
if you have just 1 link you could do it with the main timeline using the stop and goto commands (and the rest of the page would also be on all frames used for the animition), but as soon as you need 2 or more then it would become ether impossible or a bloody mess and movie clips seam to be the answer to this.
Movieclips are useful for a variety of reasons, including the purpose you mention. Anything that needs to be controlled or animated independent of other objects is usually best done in the form of a movieclip... something you can assign a name to and/or build an animation in.
what would happen if you had 100 frames of animation on the maintime line and in a movie clip
but the movie clip was only present on the first 50 frames of the main time line?
would it vanish after frame 50 and the remaining animation within the clip not show
The movieclip will only display in the 50 frames of the main timeline that it occupies. So if the main timeline moves beyond where the movieclip is, the movieclip is gone. You could stop in any one of the 50 frames that the movieclip is in and the movieclip could play thru entirely.