To update your minecraft.jar file by hand you can use google for a comprehensive tutorial for your OS (update minecraft.jar *your_os*)

You need to download the minecraft.jar file for v1.0 and update the file on your local computer.  For windows its usually in documents/settings/.minecraft/bin/minecraft.jar or some folder like that.  Use the above method for more detailed instructions.

Here is a link to my own minecraft 1.0 jar file (jar stands for java archive)