sudo useradd -d /home/testuser -m testuser admin
sudo passwd testuser
the admin at the end makes testuser part of hte admin group. you do not need to add it to the end. you can also just edit the /etc/group file and manually add testuser to the admin group.
info from here: http://www.howtogeek.com/howto/ubuntu/add-a-user-on-ubuntu-server/
http://ubuntuforums.org/showthread.php?t=201468
http://linuxservertutorials.blogspot.com/2008/11/ubuntu-create-group.html