I was just wondering if only the "official" developers have permission to commit changes to files in the SVN repository, because I was interested in contributing bug fixes whenever I could, without having to be in the development team.

Right now, for example, there is a small syntax error (unexpected } symbol on line 78) in the emoticons.php layout file, which I found when I installed 0.90; and I wanted to help, but I was denied access when I tried to commit the updated file.

Currently only the devs can commit changes. This is to stop random people from doing all sorts to the code. If however it is someone I trust, then I will add them for bug fixes etc.
Arwym, register an account on XP-Dev and post your username here. I will ask banancanard to add you so you can commit