[xwiki-users] ACL Mgt. puzzles me

Hi, I've just updated my own installation to the version 1.5. The installation itself was painless, but the XAR integration wasn't. First I had to upload the new XAR so I can benefit from the new stuff and afterwards I had to upload my own exported XAR from my old installation to preserve my preferences. I had to figure out which one to take and which one not (content, preferences, apps all together), it's like shooting a moving target (did I something wrong or is that the standard procedure?). Currently it doesn't load the user and the group part in the administration section correctly, meaning no content (FF3, Kubuntu 8.04, Opera loads it just fine), but this is maybe an issue with my PC. However, as I don't want my XWiki accessible by public and certainly not open for registration, I'm a bit puzzled about the right-scheme... How can I disable user registrations? Thanks, Squirrel