Did you really download developer (JDK) version? In user version (JRE) there is no 'javac' command. javac use to be located in $JAVA_HOME/bin (%JAVA_HOME%/bin in Windows), so you should add "%JAVA_HOME%/bin" to PATH environment variable (recommended) or use full path:
First of all I want to know you are developing Java Program manually or by using IDE. If ur using NetBeans IDE then Download the Latest version 7.2
and then there is no need to set the classpath.But if ur using manually then u have to set classpath. Bin to path environment & lib to classpath .then go to command prompt type Javac then u will supporting files will come. Then ur program will run.