If you want to use a Raspberry Pi as a 3D print server then it's best to mount it on your printer to free it from the PC's umbilical cord.
This is a surface mountable Raspberry Pi case that has it's holes pitched to suit the Orca 0.4x from Mendel Parts.
Models derived from http://www.thingiverse.com/thing:30646 by Conseils
Print Base out and mount with M3 screws.
Print either the Gyrobot Logo'ed lid supplied here or the Raspberry Pi version from original above.
Lid and Base should snap together but small pilot holes are provided on sides that can be opened out for screws.
For the 3D print server software, I have installed both Repetier Server edition and Octoprint (current favourite) running on Raspian Wheezy OS which enables you to access the printer controls and upload gcode via their respective web interfaces. Octoprint has the advantage of being able to integrate a webcam and timelapse facilities into their software.
For the Pi, I suggest Edimax EW-7811UN 150Mbps Wireless Nano USB Adapter from that well know supplier named after a river. to get rid of that PC umbilical cord forever.
Lastly I installed TightVNC on the Pi to enable me to access it's Raspian Wheezy desktop, this is optional, but useful.
More info on my Swindon Hackspace Post