Working with Vocals/Acapella 's

Hey Folks,

Can any one give me any advice on warping vocals for laying down in a arrangement and also for using acapellas if doing edits to tracks e.g adding well known vocals on to other tracks!

Would be well grateful for any links or advice…

Even a tutorial would be brilliant.

PS: Im happy getting 1 bar/2bar acapellas warped to fit in to track but not full files of vocals.