How much work would it be for you to change that first control in the 
  upper left of the dialog -- ie, where the sentence goes -- from read-only 
  to editable?  
-- nothing a little gtk_text_set_editable() can't cure -- but I have no idea 
what the corresponding BeOS widget capabilities are.  Thomas?  
If not, then this'll have to wait until we have an editable XP preview 
widget based (however loosely) on our existing view code.  Long-term that's 
probably our ideal solution, but I'm itching to do something now, so long as 
it won't turn into an implementation nightmare on one of the other
platforms.  
The reason I ask...
-------------------
After grovelling around wiring up all the pesky Win32 behaviors for this 
dialog, I finally think I understand how the W97 UI works here.   
It's really sweet.  :-)
Basically, their UI designer has come up with a really tight, clean-looking 
UI by getting rid of the "Change to" field entirely.  Instead, they've 
folded that functionality into the colored sentence preview by simply making 
that preview editable.  
I'm seriously motivated to do the same thing for AbiWord.  Soon.  Not only 
is the look and feel cleaner, but I think the platform algorithms are even 
easier to code than what we've already got.  
1.  Instead of trying to sync the edit control with the suggestion list, you 
just watch for changes to the sentence.  If there are any, you disable the 
ignore set of buttons (just like we currently disable the change buttons 
when there aren't any suggestions).  
2.  Likewise, instead of trying to replace just a single word when the 
change button gets hit, you replace the entire sentence.  Restart the spell 
check at the beginning of the sentence, and voila!  You're there!  
(There are a few more details but that's basically the idea.)
I know I shouldn't be messing with this so close to shipping 0.7.6, but 
until Shaw has the XP logic fleshed out for the paragraph dialog, I can't 
help it.  :-)
Paul
motto -- ruthlessly eliminate GUI clutter, then usability-test the result