1) It is not necessary to install "world" to run a jail. All you need are the programs (and libraries) that you actually want to run inside the jail.

2) A jail does not really need a seperate IP address. Actually, you can run many jails on the same IP address, as long as the services in each jail run on different port nrs.

An example document on how to create a BIND (mini-)jail can be found here:

http://www.bzerk.org/documents/bindjail/

Ruben