Thanks for the screenshots.  It's a great way to figure out what 
functionality we'll need on the other platforms.  
A few questions about how this dialog is intended to work (in comparison to 
the one in Word 97, for example):
1.  I presume you've added the "Change to" field so that the sentence 
display field doesn't have to be editable, right?  If so, that's a 
reasonable design choice for now, since doing it the other way would be a 
lot more work.  
2.  How committed are you to your reordering of the buttons?  GUI designers 
get pretty finicky about issues like this because of how they affect the 
user experience, so I want to make sure I understand the rationale behind 
your design.  
For example, it seems as though the UI designer for W97 optimized the 
context menus for misspellings (putting the best suggestion first), and 
optimized the dialog for unrecognized valid words.  Also, by grouping the 
change buttons next to the suggestions, it makes clear that the top half of 
the dialog is for valid stuff (that spell check didn't recognize) and the 
bottom half is for changes being suggested.  
3.  Likewise, in places where your button labelling diverges from W97's, are 
the differences meaningful?  
4.  Also, it looks like you intend to allow people to swap existing custom 
dictionaries right on this dialog.  
W97 hides this along with a number of other spell-related configuration 
stuff in a separate options dialog.  This does mean that the functionality 
is a little less accessible, and it favors the idea that most words go into 
a single current dictionary.  Doing things their way means that you have to 
go through an extra step or two to add, swap, or delete dictionaries, which 
suggests that their UI designer believes that people don't want to do that 
very often.  
Have you put that functionality here to avoid needing the extra dialog, or 
because you believe that swapping dictionaries is a common enough activity 
that people shouldn't have to do those extra clicks?  
Paul
PS:  Please don't get discouraged by this nit-picky feedback.  The work 
you've already put into getting this dialog up and running is impressive, 
and I really appreciate what you've done.  
This sort of fine-tuning to make sure that dialogs work as smoothly as 
possible for our target user -- the oft-cited church secretary -- isn't very 
interesting on the coding level, but all these subtle details really add up. 
When we're done, the cumulative effect can make a huge difference in the 
day-to-day usability of the product.