1. Go to Start > Run
2. Type in %appdata%
3. Extract "Minecraft.Alpha.1.1.2.&.SMP.LAN.SERVER.&.NAME .SPO OFER" to "appdata\roaming"
(You already should be there when running %appdata%, if not verify location)
/thanks
Open your appdata folder, copy the "cracked" client files into the ".minecraft" folder.