The list of installed JRE's is empty, when I click "add" the only options I'm given are - Execution Environment Description, Standard 1.1.x VM, Standard VM.
There's no option for a MacOS Default JRE and choosing standard VM results in the usual "Standard VM not supported on MacOS".
Eclipse Galileo, Mac OS X 10.5.8.
Any suggestions much appreciated
If you want OSX's built-in JVM, then you can add it as a Mac OSX VM, else the comment of VonC tells you what to do.
I just had the same problem and I was able to fix it. I had installed Eclipse for PHP (PDT) because I couldn't get PDT to work with Eclipse classic. I then found out that with the new install, Java files won't run! But there's a simple solution:
Go to Help->Install New Software...
Select:
Galileo - http://download.eclipse.org/releases/galileo
Under Programming Languages choose:
Eclipse Java Development Tools 3.5.1.r351_v20090810-0600-7r88FEoFI0WTo6Az-1qFRHm37ChJ
Install and you'll find your JREs!