It is not uncommon to have many different JREs running on the same machine at the same time. To check the current default version:
Open a command prompt.
Type java –version.
You will see output similar to this:
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0-b91) Java HotSpot(TM) Client VM (build 1.5.0-b91, mixed mode)