LimeWire recognizes JRE's that are listed in the Registry. There must be an entry at HKLM -> SOFTWARE -> JavaSoft -> Java Runtime Environment -> "Current Version". The value of Current Version (for example '1.5') must point to an entry under 'Java Runtime Environment'. That entry must have an entry of 'JavaHome' and 'RuntimeLib' pointing to the appropriate JRE directories.

All normal JRE installations create these registry keys.