SMPS PCB Design Signal Integrity
EAGLE is a schematic capture and PCB layout tool, not a circuit simulator. If you want to be able to simulate your design, you will need some sort of simulator. I and many others on this site like LTSpice since it is free, relatively easy to use, and most importantly free. 

Designing a 150W SMPS is not trivial and will require understanding of the physical layout effects of the PCB on the operation of the circuit. You will likely need to take an iterative approach; design a circuit to work in an ideal situation, find suitable components, layout your PCB and extract the physical connections back into the simulation model until you find something that works. To help push you in the right direction, there are dozens if not hundreds of application notes from the likes of TI, Linear Tech., Maxim, ST, etc. that describe good PCB layout techniques for SMPS.

SMPS design is not complex in principle; you simply need a switch and an energy storage element, with a feedback to your switch. The devil is in the details though, and while you may want or need a higher switching frequency to handle the power level you're talking about (and to decrease your inductor size), those higher switching frequencies will require more careful PCB design.

One more note about software, if you are a student and/or non-commercial you can get very good deals or free software from a lot of vendors. Sometimes a little groveling to a sales rep can help too ("I'm a poor college student and I need a license of HyperLynx to do SI analysis on my capstone"). If that fails, there is probably a suitable free software alternative that may not be a fancy but will probably work ok for you.