Arduino robotics, arduino boards

So I'm very new to the arduino world. I'm working on a prototype robotic arm that I want it to be programmed like an assembly robot but I'm not sure where to start off at. I was wanting to know what boards and attachments I would need?

How about starting with an existing arm and modifying the electronics to have Arduino control the switches? See OWI-535 arms http://www.owirobots.com/store/index.php

Thank you for the reply back. I already have the OWI robotic arm and its awesome but I need a six foot robotic arm and very large servos but I'm not sure what kind would have enough torque.

but I need a six foot robotic arm and very large servos but I'm not sure what kind would have enough torque.

You might check out the below project.

http://www.instructables.com/id/Giant-Computer-Controlled-Robotic-Arm-Made-of-Old-/?ALLSTEPS

After I get my robot set up what would be the best boards and hardware to run it so it can be a closed loop.

I think you need to clarify what you plan on using this robot for; after all, that large cardboard robot arm that zoomkat posted would meet your size requirements (maybe with a bit of scaling up), but if you plan on using it to weld a car chassis together - it won't have anywhere near that capability. So speed and weight handling capabilities (along with how fast you want to accelerate the weight) - all play a part. Not to mention the needed/wanted lengths of the arm segments (and their weight)...in fact, there are a ton of additional factors which I wonder if you have considered at all...?

Also - what kind of robot arm geometry have you decided to use for the task? Some geometries are easier to develop than others (for instance, a cartesian arm is decidedly easier and cheaper to build than a revolute arm).

There's also the number of joints (degrees of freedom) you require - as well as what you want to use for the end-effector (a gripper? a suction cup? a magnet? a welding torch? a paint spray gun?).

As far as hardware - besides the actuators (which again may depend on what you plan to use the arm for and your geometry), you need positional feedback from the joints (so you know joint angles); at that point, you just need controllers for the actuators (different depending on the actuator type), and a board to control those controllers - depending on the number of joints, it could be as simple as a standard Uno, or something more complex (even a standard Uno could be used for most complex control - if the joint controllers are "smart", and can be arranged/connected in a bus topology, so that few pins on the Uno are needed).