At the Pohang Accelerator Laboratory (PAL), there is a 2.5 GeV S-band linac which is under operating as a full energy injector for the Pohang Light Source (PLS) storage ring. By installing a new electron gun, a new 0.5 GeV linac, and two new bunch compressors, the PLS linac can be used as an FEL driver for the PAL XFEL project. To saturate 0.3 nm wavelength PAL XFEL SASE source, we should supply high quality electron beams to a 60 m long undulator. In this paper, we describe a new linac layout for the PAL XFEL project and its various start-to-end simulations from the cathode to the end of the linac.