Interestingly, I've just noticed that I can cause the same problem
with SlideShow under XP by changing the "Active Window Border" property.

With XP, right click on the desktop. Select Properties from the popup
menu. Find the "Appearance" tab on the "Display Properties" dialog.
Find the "Advanced" button on that tab. In the "Item" dropdown list
box, select "Active Window Border". Next to it, choose something much
larger than "1", like, say, "6" for the "Size" of the Active Window
Border. OK, OK.

Now bring up SlideShow, and load enough images into its client area
that a scroll bar appears. Notice that the scroll bar is partially
obscured by the non-client area's window frame, in the same way as my
Vista screen shot shows.

I know, I know -- why would anybody pick such a thick Active Window
Border? But Vista does by default. (In fact, I've just checked --
interestingly, that thick border is what Vista calls "1", so you can't
make it any skinnier than it already is!) It's up to you of course,
but I'm guessing you'll probably want to address this before Vista is
generally available.

Brian
-=^=-