Here is the error I get when running the client. I have downloaded minecraft.jar, and placed it as instructed in the lib folder. When the client updated, the client stopped working, and I recieved this error message:

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
Starting java from "C:\Program Files\Java\jre1.6.0_01\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(Unknown Source)
        at java.security.SecureClassLoader.defineClass(Unknown Source)
        at java.net.URLClassLoader.defineClass(Unknown Source)
        at java.net.URLClassLoader.access$000(Unknown Source)
        at java.net.URLClassLoader$1.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClassInternal(Unknown Source)
========================================
Warning: lib\minecraft.jar not found.
Did you read instructions / download it?
========================================
ERROR: Failed to run minecraft
JAVA6="C:\Program Files\Java\jre1.6.0_01\bin\java.exe"
Press any key to continue . . .

Does anyone have a solution for this problem?