i am tottaly noob to this i never design a pcb before
That is an pretty complex project for a beginner...
Should i take the eagle files of MEGA and W5100 shield and work with them?
Yes. (or see below.) In that case, you'll need Eagle. A paid version of Eagle, since the MEGA board is larger than the maximum size that the free version will do.
is there any other ready PCB schematic that includes those 3 components?http://www.freetronics.com/collections/arduino/products/ethermega-arduino-mega-2560-compatible-with-onboard-ethernet
has 2560 and ethernet. You'd have to add the time chip.
i need one piece of PCB with all of there embedded ... 3 units for test and 50 if things goes well
Why? Part of the point of a shield-based environment is that you can kludge together a multi-board demo, a lot quicker and cheaper than designing a custom PCB.
The companies that make PCB can import the smds as well?
You mean do the assembly for you? Some of them can.