Ok so this post is for anyone who has updated to 1.3 but wants to still be able to play opticraft
. If you click the link below it will take you to a mediafire page from wich you will download a file called "minecraft.jar". Once you have downloaded this read the instructions below the link.
http://www.mediafire.com/?f0zpov99n1nk1xkINSTRUCTIONS
1. Click the start button and search %appdata% and click on some thing that will Say roaming.
2. Double click on a folder called .minecraft and then double cklick to a file called Bin.
3. Delete the file called minecraft from the bin folder.
4. Now copy the file you downloaded from the link and paste in the Bin Folder.
5. Now your client should be a minecraft 1.2.5 Client.
6. When starting the game decline the update.
You should now be running 1.2.5 on your client.
EDIT: Added Some Pictures