As far as I am aware the built in TreeView check boxes are either all On or
all Off.  Perhaps someone else can shed additional light here.

I had a similar problem a while back where I had a tree that went to 4
levels. Our customer wanted to be able to select nodes only from the 3rd or
4th level, and did NOT want to see the check boxes anywhere else. The were
concerned that it would confuse users by letting them think that is was
possible to check items on the top two levels.

I solved the problem by binding an Image List control to the TreeControl,
and designing my own images for each level.  I used an empty and a checked
check box for the 4th level, an empty and a checked blue folder for the
third level and a empty yellow folder for the top two levels.  I used the
appropriate image as I built the tree, and coded a bucket full of logic in
the node click event to change the image(s) as necessary.  It was a fair
amount of work, but the results were much more pleasing and less confusing
than having check boxes available at all 4 levels.

Hope this helps.

Ron W