Upgrade/Multi-site config caused node access problems/strangeness.

I have recently created a central Drupal site for myself (http://drupal.rainbow-it.net), from which my intention was to hang off all my other sites (for ease of upgrading etc).

However, since moving one of my sites to this config and upgrading, I see some strange behaviour.

• non-authenticated users do not see my front page (I have 2 pages published to the front page - 1 for everyone and one for authenticated users). They see the "Welcome to your new Drupal website!" message instead. See http://insomniac.me.uk
• When non-authenticated users visit nodes that they do not have the privilege to view, they see the number 2 instead of the access denied message or login screen. See http://insomniac.me.uk/home-utopia

I have seen various issues in the forum about similar problems to the persistent "Welcome to your new Drupal website!" message, but none in the 'issues' area, that are exactly like I am seeing or that are either resolved or acknowledged.

System details: -
Drupal 5.1
Configuration file Protected
Cron maintenance tasks Last run 4 min 37 sec ago
You can run cron manually.
Database schema Up to date
File system Writable (public download method)
GD library bundled (2.0.28 compatible)
MySQL database 4.1.21
PHP 5.1.6
Unicode library PHP Mbstring Extension
Web server Apache/2.0.59 (FreeBSD) DAV/2 PHP/5.1.6 with Suhosin-Patch mod_ssl/2.0.59 OpenSSL/0.9.7e-p1

I thought that this might be a category problem, but I did not have the category modules installed. I installed them as I do want to use them.

The parent of the multi-site is in /data/www/drupal
The site I use most and was finding these problems on is located in /data/www/drupal/sites/insomniac.me.uk
The 2 sites use MySQL DataBases named drupal and insomniac respectively.

I would be delighted to see if there was a 'how-to' for multi-site setups like I have attempted here (especially if I have been numpty). If more information is required, I am happy to provide as much as is wanted.