You have java 6 and you need to be using java 7. Also if you have a 64 bit os then you should be using the 64 bit java. If you have a 32 bit os then you will have issues with running the dw20 pack because it requires a minimum of 2gb of ram to be allocated.
Get the latest java from the link below. Remove all existing versions then reboot then update to the latest one from the link below. Use the x64 one if you have a 64 bit system.
http://www.oracle.com/technetwork/java/javase/downloads/jre7-downloads-1880261.html