i suppose you don't want micky mouse vocals so get some software wich lets you timestretch and pitch-shift. (it will let you speed up or slow down audio without changing the pitch. Or it will let you change the pitch without changing to lenght so you have total controle.) (soundforge should be able and a lot of other sample editors) or you can look for something like Timebandit (by steinberg) or Timefactory ( by Prosoniq (up to 30% stretch or compression without audible artefacts.. but you pay the $$$ of course.).) these are standalone applications but offer a very good quallity and in time-strectching. the quallity of the algorythms is of vital importance.
You'll need a bit of a multi-tracker to match and position the vocals on the beats well, but soundforge should be Ok for something like that unless you're going to re-arrange the track. (wich of course isn't a problem, you just need some more powerfull software.)