Firstly, in eBox at least a user, for instance "john", with the jabber account enabled must be created. In Jabber section, you must set a domain, for example, "jabber.example.com". The SSL support is important, require SSL. Finally, enable the jabber service. Now let's go to the client side.
In Pidgin, I use 2.2.0, you must configure a XMPP account. In basic settings, the user name must be "john", the domain "jabber.example.com" and the password, the user's password. In advanced settings, you must check "Require SSL/TLS" and as connection port "5222" with the IP address, the address from any of your interfaces. These two last settings may be avoided if you set the DNS server accordingly or edit manually for "/etc/hosts" by appending the line as follows:
# Provided that the internal interface IP address is 192.168.1.1
192.168.1.1 jabber.example.com