For some reason I fail to understand the recently released collection of plugins from the Eclipse Foundation (also referred to as Callisto) doesn't include support for XSLT even though it has editors for XML, DTD's and XML Schema (XSD). Support to XSLT is however very easy to add since you can use the EclipseXSLT plugin.
Installing is as easy as creating a new remote update site under "Help\Software Updates\Find and Install" and installing it from there. The address to the update site is http://eclipsexslt.sourceforge.net/update-site. Took me 5 minutes or so. Easy. It does however require that you already installed the XML part of the Callisto release.