Hi, it's funny how you say "has to install some kind of open source program" well, let me remind you that aMSN IS an open source program and that's why you're even able to do what you do with it
Anyways, there really a lot of people who use aMSN SVN and who are really complete newbies (average and under-average Joes) and they never had any problems with getting SVN installed.. however I think that maybe it's because the average Joe uses the development archive way instead of the SVN method.. unfortunately, when you looked, that method was not available in the wiki because it linked to the old mac forums which are now deprecated and unused and the thread disappeared..
Thankfully, TomH. had a copy of these instructions and I've updated the wiki with the instructions.. so go back to http://amsn-project.net/wiki/Installing_SVN#The_development_archive_way
and have a look at the development archive way, follow the instructions in the screenshots and you should get aMSN SVN working without any troubles!
Hope it helps!