Just a quick question. Anyone out there know the best way to fix a mech whose torso/arms wont move?

Yup. Don't move em' :p or force them and if hey break pin them back in a position you like, or mail em' back to wizkids to replace.

One thing that works on about 75% of the "stuck" minis I've ever had is to apply pressure INTO the joint - do NOT twist if you can help it, as it will break off - it's kinda like the best way to remove a tooth... ow..

Sometimes I freeze 'em for a few hours. If there's any glue in the joint it becomes slightly brittle. If not, it firms up the plastic a bit. Putting them under a hair dryer works, because the heat will slightly expand the plastic around the point of rotation before heating up the pin itself.

Sometimes I've used simple dishwashing detergent applied to a thin tool such as the dull (unsharpened) edge of an exacto blade. Run the tool along the joint, as deep into it as possible, from every side possible. And then gently work the joint back and forth... very gently. The detergent work it's way in, and lubricates the joint without causing any harm to the paint job.