Mediawiki will not configure

Binary package hint: mediawiki

I've installed mediawiki on Ubuntu Jaunty server 64:
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uname -a
Linux 2.6.28-13-server #45-Ubuntu SMP Tue Jun 30 22:56:18 UTC 2009 x86_64 GNU/Linux
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Surfing to localhost/mediawiki takes me to a config page. After filling in the config details, I get this:
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MediaWiki 1.13.3 Installation

    * Don't forget security updates! Keep an eye on the low-traffic release announcements mailing list.

Checking environment...

Please include all of the lines below when reporting installation problems.

    * PHP 5.2.6-3ubuntu4.1 installed
    * Found database drivers for: MySQL
    * PHP server API is apache2handler; ok, using pretty URLs (index.php/Page_Title)
    * Have XML / Latin1-UTF-8 conversion support.
    * Session save path (/var/lib/php5) appears to be valid.
    * PHP's memory_limit is 32M.
    * Couldn't find Turck MMCache, eAccelerator, APC or XCache; cannot use these for object caching.
    * Found GNU diff3: /usr/bin/diff3.
    * Found ImageMagick: /usr/bin/convert; image thumbnailing will be enabled if you enable uploads.
    * Found GD graphics library built-in.
    * Installation directory: /var/lib/mediawiki
    * Script URI path: /mediawiki
    * Installing MediaWiki with php file extensions
    * Environment checked. You can install MediaWiki.
    *

      Generating configuration file...

      Notice: Constant MW_INSTALL_PATH already defined in /var/lib/mediawiki/config/index.php(741) : eval()'d code on line 19
    * Database type: MySQL
    * Loading class: DatabaseMysql
    * Attempting to connect to database server as root...success.
    * Connected to 5.0.75-0ubuntu10.2; enabling MySQL 4.1/5.0 charset mode
    * Attempting to create database...
    * Created database wikidb
    * Creating tables... done.
    * Initializing statistics...
    * Granting user permissions to wikiuser on wikidb...success.
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Surfing to localhost/mediawiki takes me back to the config page; there's no way of actually getting to the mediawiki. The behaviour I'd expect to see is to be able to use the Wiki.