You need to build OTcl and Tclcl prior to ns-2. This is because ns-2 uses both of them not only during execution but also during the compilation. More, Tclcl depends on OTcl so you need to build the packages in this order: OTcl, Tclcl, ns-2.

There are several ways of installing the applications - one is very easy, but is not right for Ubuntu. However, There is an 'upgraded' version that makes the first method suitable for Ubuntu (suitable doesn't mean 'the way it should be done').The other one is much longer but is more Ubuntu-aware.

As for the first 'not right' does not mean that it won't work, it's just not the way Ubuntu or Debian developers believe to be proper (and they are probably right). More, it can lead to some problems in the future in case of upgrading ns-2 or the other 2 packages.

The second method - it creates debian packages, but doesn't mind dependancies and so on...

The third method will take some more time but it would be much easier for you to upgrade ubuntu or ns-2 in the future.