Just drop http://lilypondtool.organum.hu/LilyPondTool.jar to your .jedit/jars directory (inside your home folder like c:\Documents and Settings\John\.jedit\jars).
It still supports the latest stable LilyPond, 2.12, but as soon as LilyPond 2.14 stable is released I will release a new version of LilyPondTool (also in jEdit plugin repository).
The most important new features of this LilyPondTool release are the following:
- better context-sensitive completion
- musicglyph preview
- template manager with context sensitive completion and BeanShell, Velocity support
- preview in wizard
- customizable background for the PDF preview
- help in context menu
- localization manager
- compile without saving