Try placing the new carpet face down then center the old one on top also face down, this keeps the nastyness off the nap
Mark the hole for the e-brake with a marker, then cut a smaller hole in the new carpet, the rest is easy from there,
If you go over to the fox forums, better yet, I'll just move this,
It's also a good idea to checkout the floors for rust/damage and maybe add some sound deadener/insulation.