How do I set environment variable in a build definition properties tab before running my build?

I went to the properties tab in the build definiton and set five enviornment variables here.  My build failed because it could not find my JAVA_HOME environment variable.  However, I thought I had set that correctoly in the properties tab.  Here is what I did:

Name:  JAVA_HOME

Value: C:\projectA\spin16\java7\jdkl1.7.0_25

Any suggestions as to how to set an enviornment variable using the build definition properties tab?

Thanks.