You can find your minecraft.jar file on a windows PC by clicking on start in your toolbar at the bottom of the screen and click 'Run'. If the 'Run' button isn't there, use the search bar a the bottom of the start screen and search 'Run'. Then a Window with a text box will come up, in the text box you must type inand then you need to click on .minecraft and then click bin. In the bin folder you will see a file called ether 'minecraft.jar' or 'minecraft'. To open this file, You must have WinRAR archiver or 7zip or whatever. You can get WinRAR archiver at the link under "Sources and related links" below this answer.
You can find canning jars in some grocery stores, some hardware stores or some places like Walmart. It depends where you live. If you cannot locate any locally, you should try online sources.
premium: get the 1.0.0 Minecraft jar here modsforminecraft.com/ and delete the Minecraft jar that you have and put the 1.0.0 jar in
find a .minecraft folder with zombiecraft already installed then replace it with your normal .minecraft then run the .jar file but DONT force update (minecraft 1.1)
You need an a jar from alpha stages, which you can get with Minecraft Nostalgia.
download it then chuck its contents in a mods folder in minecraft .jar
You need to have java 6 or later installed on your mac for a minecraft server jar to open correctly. If this doesn't work you can use a terminal command to run the jar.
premium: get the 1.0.0 Minecraft jar here modsforminecraft.com/ and delete the Minecraft jar that you have and put the 1.0.0 jar in
on windows on the folders thing at the to type in %appdata% then go to .minecraft than bin then delete the minecraft jar in it then put the 1.4 jar in
find a .minecraft folder with zombiecraft already installed then replace it with your normal .minecraft then run the .jar file but DONT force update (minecraft 1.1)
MinecraftServer.exe/jar
You need an a jar from alpha stages, which you can get with Minecraft Nostalgia.
download it then chuck its contents in a mods folder in minecraft .jar
You need to download the pre-release jar and replace your other jar with the pre-release jar.
There is one way, and one way only. You need to find a download containing either a .jar file or the full on .minecraft file of the desired version. Go to %appdata% (When you type it, it will take you to the appdata folder) Then either Delete the current .minecraft or go deeper and replace the .jar with the one you want. Remember to back up newer maps for they can be corrupted with an older minecraft.
You need to have java 6 or later installed on your mac for a minecraft server jar to open correctly. If this doesn't work you can use a terminal command to run the jar.
le find dust.swf or dust.jps . then copy and paste the link
delete your BIN and then run minecraft, it will then be cleared and restored, this doesn't change your worlds.
You have to open it with winrar.