The above user was correct in identifying the registry key:

HKEY_LOCAL_MACHINE->SOFTWARE->Javasoft->Java Runtime Environment->CurrentVersion

as the one that we check. We check for the presense of 1.3, as this is the version that LimeWire is really tested with. LimeWire will work with 1.4, although we have not thoroughly tested it with this platform. You can, however, install LimeWire and then uninstall the 1.3.1 JRE. For LimeWire to work after doing this, though, you would have to change the targets of all of the shortcuts to point to your jave 1.4 version of javaw.exe.

Note the parts of the GUI will look a little funny, but you might see some nice performance improvements.