Working for me, Tekkit 2.1.1
There is a fix, see this thread here:
http://www.computercraft.info/forums2/index.php?/topic/612-computercraft-131-for-minecraft-11-backport/
You will need to update both the server's and client's files, and make a change to a config file. Use the bukkit version for the server and the client for clients/users.
On both versions, you need to change the item ID for the turtle to avoid a conflict crashing the game/server on startup. Here's how:
Client:
1. After updating, open this file: %AppData%\.techniclauncher\tekkit\config\mod_CCTurtle.cfg
1b. If it isn't there, try to run the game and it will create it (and then crash), then open it.
2. Change the item ID so the line reads as follows:
turtleBlockID=214
(You may have to adjust it if you have made other changes, just give it an ID that isn't too big or taken by something else. Easier said than done, yes.)
7. Done. It should work now in single player or on a server with the respective update.
Server: (again, after updating)
0. You should probably delete both of these so it can remake them proper (just in case):
/config/net.minecraft.server.mod_CCTurtle.cfg
/config/net.minecraft.server.mod_ComputerCraft.cfg
1. Edit the item ID in "/config/net.minecraft.server.mod_CCTurtle.cfg" to the same as what the clients will be using (214).
82. Done.
Optional: There's a neat new feature in this version that allows you to get programs from pastebin in-game.
To enable it, change this in "/config/net.minecraft.server.mod_ComputerCraft.cfg":
enableAPI_http=1
Ok bye.
