What do you mean by free memory? Free RAM available in your PC or free space left in the java heap? Free RAM is not a very good indication of anything since the OS decides how to allocate that space, and what applications/services to run. You really should be looking at memory allocated to the java process to see how much memory the jboss app server is using.
my apologies on the confusion. I am talking about the java Heap. I am using -Xms768 and -Xmx 1536 into my startup script.