synching up acapellas.

when you have an acapella say a rap or whatever. what method do ya'll use to synch it up to your beats.
for some reason it is hard for me to get it exactly synched right.
then again maybe i am just retarded.

heres what you do...

get the origional track

SAMPLE the og rap track, with the old beat in it for however long you need.

now, just go to the screen where you view the waveform
EDIT
bpm change
read where it says source tempo.
thats your bpm. set it and forget it.

thanks good idea.