Ok, script attached ... seems to be working ok for me, 
tried to install and remove a few times. It does the
right thing with the smf when installing, you can then 
simply enable the service. Upon removal it cleans up the
files but won't clean up the services (I think until
a reboot) ... I've only started looking at the new 
packages stuff in the last day or two, so I could be 
missing something, but I can't find any way to force
 a proper cleanup.

It requires that you have a writable repository setup 
as per the docs on the opensolaris website and it will
create a dnsmasq package (package name is a variable 
in the script). The script takes a version number for 
the package and assumes that it's in the contrib/Solaris10 
directory, it then works out the base tree directory 
from $0.

i.e.  $ contrib/Solaris10/create_package 2.52-1
or   $ cd contrib/Solaris10; ./create_package 2.52-1

It's a bit more complex than it could be because I 
prefer putting the daemon in /usr/sbin and the config 
in /etc, so the script will actually create a new 
version of the existing contrib dnsmasq.xml.