Version of Ubuntu is installed.?

How to know, the release version of Ubuntu installed in your system..?

$lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 8.10
Release: 8.10
Codename: intrepid

Installed package version.

How to know the Installed version of the particular package in debian..?

You can use the following command...
apt-cache show

That will list the version information.