How to animate a model in blender:
(do this in the default view)
Before you start, make sure your model is joined(no separate cubes etc.), if they aren't select them all and click join from the tool panel. Press 't' to change to wireframe mode. Then you'll need to add bones. Add one using the 'create' panel, and then(IMPORTANT), switch to edit mode and add any other bones you need. If you select the little circle on the end of a bone and press 'e', you can make a bone that is connected to the one you have highlighted. Make a bone for every part that should move, for example a head would have at least one bone. Then in object mode, first select the model, then the bones(not the other way around) and press 'p', and choose "with automatic weights" from the menu. If you're lucky this will work nicely, if you aren't you'll have to do more work. Highlight the bones and press 'ctrl+tab'(pose mode), and highlight a bone(it should be blue), then use 'r' to rotate it a bit to see if it works. Rightclick afterwards to cancel, this is just a test. Do the same for all bones. It's likely that some bones will move parts you don't want them to.
Fixing bone problems:
Staying in 'pose mode', right click the model and switch to edit mode. You can then select the face(or lines and vertices) of a moving part. Once you have done this(just for one part), find the panel on the right(or wherever you have the properties panel with all the icon tabs) and click the icon of an inverted triangle. You should then see a list of bones(you may need to make the panel a bit wider). Find the bone you need the part to attach to and rightclick it. Then choose 'assign'. If you don't know which bone to assign to, just go to object mode, then right click on the correct bone. It's name should show up in the bottom left corner. If you are trying to stop a bone controlling a certain part, you would do the same, but this time click 'remove' instead of 'assign'.
Now that the bones are assigned you can actually start animating the model. Down the bottom of the window there should be a timeline. Move the green line to 1 or 0 or wherever the start is, move your mouse over the model and press 'i', then choose 'locrotscale'. This is how you insert a frame into the animation. It's best to do this straight away so you don't lose the initial position of the model. Then you can move to a different frame(like 5 or 6) and use the bones to put the model into the right starting pose for an animation. You can move, rotate, or scale bones(although if you scale bones you can't scale the model easily afterwards). When you have done that, use 'i' to insert the frame.
You don't have to do this for every frame, just for the important ones. For example, to make a bone bend, you would make one frame with it's stating position, move a few frames ahead(like 10) and then rotate it and make a new frame. Blender will automatically fill in the frames in-between with the rotation of the arm.
Notes:
You can delete frames with 'alt+i'
You can set the end and start points of the animation, this is useful for testing.
I hope this is useful for you and that I haven't missed anything important.
Also you should keep an eye on this thread:
viewtopic.php?f=47&t=16455
Also about leafdecay, add this to the groups of the node "leafdecay=1"