Assuming all the machines can see eachother ...
get the IP address of the machine you are running runserver on. For example run ifconfig
at the console.
ifconfig
eth0 Link encap:Ethernet HWaddr 10:1e:72:b8:2a:4b
inet addr:192.168.1.2 Bcast:192.168.1.255 Mask:255.255.255.0
...
check if you are running a firewall. For example
sudo ufw status
if active, you need to open port 8000 so, again at the console, run
sudo ufw allow 8000/tcp
then start the runserver (or runserver_plus if using django-extensions)
python manage.py runserver_plus 192.168.1.2:8000
open a browser on another machine
http://192.168.1.2:8000/admin