Update to newer version

Generally speaking, in Ubuntu most packages have a "maintainer" - a person that takes care of the package (fixes reported bugs and packages new versions when they are released).

Searching for the "qgis" package in packages.ubuntu.com (<http://packages.ubuntu.com/oneiric/qgis>) and packages.debian.org (<http://packages.debian.org/sid/qgis>) and looking at the "maintainer" and "version" fields leads to the conclusion that the package is maintained by a Debian developer, imported automatically into Ubuntu and then customized for Ubuntu itself.

Your best bet would be:
1) opening a bug at the Debian bug tracker (see <http://www.debian.org/Bugs/Reporting>), requesting that the new "upstream" version should be packaged for Debian;
2) opening a bug at Launchpad as well (<https://bugs.launchpad.net/ubuntu/+source/qgis>), use a subject line similar to "Please update qgis to version 1.7"), mentioning the fact that a bug report has also been filed at Debian;
3) link the Debian bug report to the Launchpad bug report (use the "Also affects project" link in the Launchpad bug report and provide the URL to the Debian bug page).

Once the bug reports have been opened, a Debian/Ubuntu developer will have a look at them and decide if the latest version is worth inclusion (it usually is unless major dependency/stability problems are found).

Let me know if you need any further information or guidance regarding this - I'll be happy to help you.

http://www.qgis.org/wiki/Download#Ubuntu