Image Lists, TreeView, Transparant and Win98

I've got a problem, using an image list and a tree control.  

I've got a number of images (about 20), all of them 16*16 pixels and clRed
is used as the background colour

I add these images to the image list and then try show them in the
TreeView.  Unfortunatly no matter what settings I use I can't seem to get
transparant images showin in the treeview (where the red bit should be
aliased out).  

I must be doing something wrong, but I'm damned if I can figure it out!

 Taz Higgins...