Date: 2/21/2009 4:56 pm EDT
Don't waste your money buying a RotoZip. Rent a real tile wetsaw. The RotoZip will work on a limited basis but is much too light duty to last and won't cut straight lines without a straight guide of some description.
The 4" angle grinder will work but there again - too many cuts using a dry diamond blade will ruin the blade and progress will be very slow. Rent a wet saw.