I noticed that the treeview control appears to have different properties
available to it depending on whether it's used within a form or sheet in
Excel 2003.

Apparently using an image list is not possible when the treeview control is
placed on a sheet rather than a form. Not only this, but the option to
display a checkbox for each node also appears to be absent when used on a
sheet too, and this appears to be only one of a handful of options that
aren't there.

Just look at the 'custom' property dialog for a treeview on a form then on a
sheet - there appear to be 3 checkbox based options on the 'general' tab when
placed on a sheet and 8 when in a form. The 'Full Row
Select','Checkboxes','SingleSel','Scroll' and 'Hotracking' options are all
absent on the sheet based treeview options.

I'm curious: why are there these differences?