How do I install the latest version of packages in Ubuntu?

Distributions (such as Ubuntu) do QA on their packages and so will not always have the latest version of everything available in their repositories as soon as they come out. The emphasis is on stability.

If you really need a more recent version for some reason, you can use Python's own package management stuff (setuptools, in case you need to install it), like so:

python easy_install numpy

This will install the latest version available on PyPI.

I would recommend removing the package installed by the distribution first, since they probably don't play well together in the event of conflicting paths.

As Ubuntu is released every 6 months, Cannonical includes the latest stable version of a package when they begin testing of the next release. For example, even today (Jan 2010), Ubuntu 8.04 LTS still runs Firefox 3 rather than Firefox 3.5.

There are some intrepid hackers who want Firefox 3.5 on ther Ubuntu 8.04 LTS, and these people are able to obtain and maintain mini-repositories on Launchpad. For example, here is a link explaining how to use a Launchpad repo to get Firefox 3.5.

As it turns out, numpy has a launchpad PPA repository, in fact it has three, one for Jaunty, one for Intrepid, and one for Hardy. But, these Launchpad PPA releases happen to be older versions (current for 9.10 is python-numpy 1:1.3.1-3, the PPA releases are 1.2.1 or 1.1.1). If you want the latest version of numpy available from a repository, you may need to seek fame and fortune as an intrepid hacker and put together a Launchpad PPA for the version you need.

I have been very thankful for the things people have put on launchpad, not being an intrepid hacker myself.