Hey there.  As far as I know, Betterman cels 
aren't too tough to find.  At least they haven't 
been in the past...  I have one from it, even 
though I really don't know anything about the 
series.  I'm on the public computer right now, so 
I can't directly post the image of the cel that I 
have, but here's the link if you wanna see it at 
my Rubberslug site:

http://rekka.rubberslug
.com/gallery/inv_info.asp?
Gallery=rekka&ItemID=6091

Sorry, I don't know about .hack...

Rekka