try chopping the accapela into shorter sections like 8, 4 maybe even 2bar peices. its really unlikely that u'll get the lyrics synced over a whole song unless ur absolutely bang on with the tempos but by chopping it u'll give urself slightly more of a margin of error
WWW.MYSPACE.COM/BASSWEIGHTPRESSURE - - - Dubstep / Dub / Grime
Try it......you might like it