Question: Can I make the hand stop when it runs into a certain body part?  Example: Making the palm stop on the character's hip automatically.
Answer: Yes.  In the upper right hand corner of the "Preview" window is a small arrow pointing to the right.  Right click it and a menu will popup.  On the bottom of the menu is an option for "Collisions".  Turn Collisions to "on".    Now go to the properties for your character's "hip" and turn on "Collision detection".  Now go to the properties for your character's "right hand" and turn on "Collision detection", now attempt to move the right hand through the hip. You can't.  This makes life much easier when posing.  Try it with the right leg/left leg as well.  NOTE: You may have to turn collision detection on/off in the top right menu, sometimes objects will get stuck inside each other.  I tend to juggle between collision detection on/off when posing.

Question: How do I move my characters hands only so that the arms follow the hand? 
Answer: Make sure that the left hand and right hand are checked under Figure---->Use Inverse Kinematics---> Left/Right Hand.  Now you can move the right/left hand around by using the xtran,ytran,ztran options under "parameters".

Question: How do I bend the knees?
Answer: Turn the left/right leg OFF under Figure ----> Use Inverse Kinematics ---> Left/Right Leg.  Now you should be able to bend the knee by selecting the characters shin.

Question: How do I move the characters leg around?
Answer: Select the characters foot and move it around using the xtran,ytran,ztran options under the properties window.  (This will not work if the inverse kinematics are off for the leg.)

I know this is basic stuff but I didn't figure it out for quite a while. I just learned how to use collision detection like a few minutes ago.

Zanzo

A note on using IK - be careful when you do and do not use it... if you have it on any body part when you apply a preset pose from the library, things are liable to go crazy in the results. :) Most folks simply turn IK off as soon as a figure is loaded, to save time. You can of course turn it on to tweak things after a pose is applied, as you've spelled out. :) /P

Another tip on collision detection: there's also a mode on the collisions menu that shows intersections, instead of preventing intersections. The main drawback of collision detection is its resource use, if you have a somewhat more complex scene, using collision detection will slow the system down to a crawl. The "show collisions" option seems to be a little less resource intensive, and it also doesn't suffer from objects getting stuck.

An interesting use of the collision detection option in objects is for dynamic hair. When the collision detection option in an object's properties is turned on, the dynamic hair simulation will try to prevent hair from penetrating that object.
Again, the more collision objects, the slower the hair calculation will be. Using low-resolution proxies greatly speeds up calculation (try kirwyn's free dynamic hair figure, and find out how fast dynamic hair calculation can be).

Tip on using IK: if IK is turned on, you can parent that body part to something else. For example, you could parent a figure's feet to the pedals of a bicycle figure, animate the bicycle pedals and the fgiure will have a pedaling animation.
Other use: let the figure grip a two-handed item (a rifle, a greatsword, a broom), parent both hands to that item, and you can pose the item and the arms and hands will go with them.
Setting "use limits" on the Figure menu is useful here, it prevents the IK calculations from returning impossible values (looks like a wrist or ankel getting badly mangled).

I hate having the figure I'm posing have some parts (elbows, knees, feet, ect.......) plunge through the ground or floor prop I'm using. I love being able to turn collision detection on the figure and ground or floor prop so this doesn't happen.

GOOD TIPS!