Notch is releasing Minecraft 1.6 later this week (ETA is Wednesday). The server will NOT be updating to 1.6 for most likely around a week after this happens.
If you want to continue playing on the server during this time, DO NOT UDPATE TO 1.6!
The file that I have attached here in my post is the 1.5 minecraft.jar file for those who updated.
Delete your updated file and copy this into it's place