Start your Eclipse.
Select Help -> Install new software...
Add SPL Tools plug-in update site:
http://sourceforge.net/projects/spl-tools/files/eclipseupdatesite/
Add Xtext update site (Not required for Eclipse Juno)
(Xtext 2.3.0 or newer required)
http://download.itemis.com/updates/releases/
Add or allow default eclipse update sites for your eclipse release.
(Eclipse Modelling Tools required for Xtext and Xtext for Juno)
Named like "Indigo" or "Juno" for your Eclipse release.
Select SPL Tools plug-in update site
Select "SPL Tools Eclipse Plugin Feature"
Install plug-in.
Note:
Eclipse Indigo does not handle referenced updates sites in features correctly, so it is necessary to manually add Xtext update site.