You must have a JRE or JDK on your PATH
in order to run Eclipse.
If you are on Windows 7, go to Control Panel > System > Advanced System Settings > Advanced > Environment Variables. Find the Path
system variable. Edit it and append the location of your JRE's bin
folder to the end of it.
Note that the JRE will be enough to run Eclipse, but to actually compile any code you will need a JDK.