I tried replacing the call, but I gave up somewhere at the end since I realized that I'm not even sure I'm doing it properly due to some regex match syntax in PHP. Sometimes $1, $2, etc. are used and some times escaped \\1, \\2, etc. are used and I'm not sure if this is it. >.<
I'll send you everything, Ryex. See if you wanna port it to SMF 2.0. I'll try to disable the deprecation warnings for now.
EDIT: Didn't work. :/ I contacted support. Let's see if they can do it. But for now the actual best option might be to temporarily switch to an old PHP version until we upgrade to SMF 2.0.
EDIT: Alright, I got a reply and the warnings are now disabled. We should really switch to 2.0 ASAP. If PHP gets updated again at some moment, it's possible that the forum will stop working. >.<
EDIT: Yup, switching is the way to go. They won't update that part of the code. :/
http://www.simplemachines.org/community/index.php?topic=528463.0Ryex, feel free to completely wreck everything. We'll figure out the additional stuff later. The theme can also go, I'm ok with that. We can always remake or update it at some point later.