[Muzoid]

simple idea is something like this but varies depending on the material...

If it's highly percussive (drums are well defined in the mix)...

Find 1st easily identifiable beat (say it's a kick at Bar 1 Beat 1, if you're really lucky), zoom in, place cursor, apple-I (identify beat), designate at 1.1.

go to end of song, if it's hip-hop and it's all 8 bar sections, go to beginning of last 8 bar section, find kick on 1, place cursor exactly as you did before, identify beat (count measures so you know what bar/beat this is) and voila PT calculates the tempo and you have a grid to work with.

do that with the instrumental, line up the main to the inst, nudge till perfect, then line up acca to main. You can do all sorts of stuff like panning the main to one side and the acca to the other and nudge the acca till the vocal seems to sit right together,

Good Luck. If you still need help, email me.