I'm using the Microsoft TreeView Control 6.0 in Microsoft Access. It seems to work very well, except that it doesn't seem to have a greyed out state, indicating that some, but not all child nodes are checked.
I've looked into using my own images to simulate the checkboxes, but if I do this, I then have to remove the real checkboxes or it looks like I have two checkboxes for each item... but then I don't have any checkboxes and I can't work out how to handle a click on the images.
I can find loads of people having the same sort of questions for this control in other languages/uses, but I can't find a solution for Microsoft Access.
I would happy moving over to a different control, if there's something else available that gives me a hierarchical structure with tri-state checkboxes.
After a bit of research and a couple of hours coding, I was able to write a solution myself.
I had to add an ImageList, associate that to the TreeView and add an image of a checkbox for each of the three states. Google Image search saved me some time here :).