Ok, at someone elses suggestion I've started a new post for this problem. If you go to http://evilmoose.shafted.com.au/russell.php - and click on any of the category links, they don't work - they return you to the main page instead (http://evilmoose.shafted.com.au). The link in the bar shows as: http://evilmoose.shafted.com.au/index.php?cat=11 for example, but all that is shown on the screen is the standard evilmoose.shafted.com.au page.
If it's relevant, I have limited evilmoose.shafted.com.au to showing category 1 posts (and I think 11 as well), and the /russell.php page shows every other category at the moment.
I've been searching online and through forums all day, and haven't been able to work out why the category links are behaving this way, I was hoping someone here could help me out.