There are actually just hands included with Poser in the Figures->Additional Figures library, although they are massively scaled upon loading so probably not ideal for what you want.

Re James, if you use the tools (rotate, twist, translate) to drag the arm around he does seem to balance himself, but using the dials (collar, shoulder, forearm and hand respectively) to move an arm doesn't result in the other arm/hand moving. Not in my experience, anyway.