I have downloaded the client from this website, downloaded minecraft.jar from the minecraft.net, but it's still a problem when i double-click the "Run".

Autodetecting java
Testing default folder
Checking C:\Program Files\Java\jre6 folder
Found java in C:\Program Files\Java\jre6 folder
Checking C:\Program Files\Java\jre1.6.0_01 folder
Found java in C:\Program Files\Java\jre1.6.0_01 folder
Checking C:\Program Files\Java\jdk1.6.0_16 folder
Found java in C:\Program Files\Java\jdk1.6.0_16 folder
Checking C:\Program Files\Java\jdk1.6.0_17 folder
Found java in C:\Program Files\Java\jdk1.6.0_17 folder
Starting java from "C:\Program Files\Java\jdk1.6.0_17\bin\java.exe"
Exception in thread "main" java.lang.NoClassDefFoundError: com/mojang/minecraft/
MinecraftApplet
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:616)
        at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:12
4)
        at java.net.URLClassLoader.defineClass(URLClassLoader.java:260)
        at java.net.URLClassLoader.access$000(URLClassLoader.java:56)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:195)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:303)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
        at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:316)
Caused by: java.lang.ClassNotFoundException: com.mojang.minecraft.MinecraftApple
t
        at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:303)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
        at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:316)
        ... 12 more
Could not find the main class: Main.  Program will exit.
ERROR: Failed to run minecraft
JAVA6="C:\Program Files\Java\jdk1.6.0_17\bin\java.exe"



And when i click edit on the "Run" it comes this:



@echo off

rem If you have a custom path to java, change auto below to
rem point to your java.exe file
rem eg:  set JAVA6="C:\MyPath\bin\java.exe"

set JAVA6="auto"

set X86="%ProgramFiles(x86)%"
if %JAVA6% == "auto" (
  echo Autodetecting java
  if %X86% NEQ "" (
    echo Testing x86 folder
    for /D %%j in ("%ProgramFiles(x86)%\jre6*" "%ProgramFiles(x86)%\jre1.6.*" "%ProgramFiles(x86)%\jdk1.6.*" "%ProgramFiles(x86)%\Java\jre6*" "%ProgramFiles(x86)%\Java\jre1.6.*" "%ProgramFiles(x86)%\Java\jdk1.6.*") do (
      echo Checking %%j folder
      if exist "%%j\bin\java.exe" (
        echo Found java in %%j folder
        set JAVA6="%%j\bin\java.exe"
      )
    )
  ) else (
    echo Testing default folder
    if defined ProgramFiles (
    for /D %%j in ("%ProgramFiles%\jre6*" "%ProgramFiles%\jre1.6.*" "%ProgramFiles%\jdk1.6.*" "%ProgramFiles%\Java\jre6*" "%ProgramFiles%\Java\jre1.6.*" "%ProgramFiles%\Java\jdk1.6.*") do (
        echo Checking %%j folder
        if exist "%%j\bin\java.exe" (
          echo Found java in %%j folder
          set JAVA6="%%j\bin\java.exe"
        )
      )
    )
  )
)

:rerun
if %JAVA6% == "auto" (
  echo ERROR: 32-bit Java 6 not found!
  echo Please download and install from java.com
  pause
  exit
) else (
  echo Starting java from %JAVA6%
  %JAVA6% -classpath skin;lib\jinput.jar;lib\lwjgl.jar;lib\lwjgl_util.jar;lib\World of Minecraft.jar;lib\minecraft.jar -Djava.library.path=native\windows -Dsun.java2d.noddraw=true -Dsun.awt.noerasebackground=true -Dsun.java2d.d3d=false -Dsun.java2d.opengl=false -Dsun.java2d.pmoffscreen=false -Xmx800M Main

  if errorlevel 11 (
    if not exist lib\minecraft.jar (
      echo ========================================
      echo Warning: lib\minecraft.jar not found.
      echo Did you read instructions / download it?
      echo ========================================
    )

    echo ERROR: Failed to run minecraft
    echo JAVA6=%JAVA6%
    pause
    exit
  )