I was going to do this manually, but after a bit of Googling I came across a script which does the job nicely. I downloaded it, had a look at the code, and once satisfied, ran it. I now have plymouth at boot.
The code courtesy of d0rkye and kyleabaker:
wget http://launchpadlibrarian.net/121675171/fixplymouth
chmod +x fixplymouth
./fixplymouth
Original article found here:
http://www.webupd8.org/2010/10/script-to-fix-ubuntu-plymouth-for.html
Thanks webupdate, d0rkeye and kyleabaker.