The sketch on the front page is indeed by Watsuki.
After I finish moving and get around to scanning
in all my new sketches I'll post the complete 
image of that sketch (there's another sketch of
Kaoru on the page as well) and the Yuki sketches
I got over the summer and recently.  Also to 
answer the other question about the Watsuki 
sketch, I got it through a trade I did with him.
He was there at SDCC to buy comic goodies as a 
fan/collector.  It so happened that him and I
shared some common interests and were able to
work a trade out that we were both happy with :)

Thanks,
Brian