You will need Java to play Minecraft. If you don't have it, go get it.
If the files show up as a compressed archive (Zip/Rar) to you, or you cannot open the file by double clicking on it, first ensure you have Java installed. If you have Java installed then try using Jarfix to fix the file association.
Proxy for the new Minecraft Launcher enabling 1.7.2. Using this, you may login with whatever username or password you want. Servers should ask you to login again once you connect.
If you get a corrupted jar error, try getting it from one of these mirrors instead:
The old proxy has been discontinued.