From Eclipsepedia

To install the GMF SDK and all its prereqs from the Ganymede Update site directly into the dropins folder, run this:

#!/bin/bash
workspace=/tmp/workspace-clean-34
eclipseroot=~/eclipse/34clean/p2director
installTargetFeatureGroup=org.eclipse.gmf.sdk.feature.group
bundlepoolDir=$eclipseroot/eclipse/dropins/${installTargetFeatureGroup}/eclipse

pushd $eclipseroot >/dev/null
if [[ $# -eq 0 ]]; then
	rm -fr eclipse $workspace $bundlepoolDir
	eclipse=eclipse-SDK-3.4-linux-gtk.tar.gz
	echo "[`date +%H:%M:%S`] Unpack $eclipse ...";
	tar xzf $eclipse
fi

vm=/opt/sun-java2-5.0/bin/java
#vm=/opt/ibm-java2-5.0/bin/java

echo ""
echo "Using:       vm=$vm and workspace=$workspace";
echo "Installing:  ${installTargetFeatureGroup}";
echo "Destination: $bundlepoolDir";
echo ""

echo "[`date +%H:%M:%S`] Running p2.director ... ";
#  -console -noexit -debug
./eclipse/eclipse -vm $vm -nosplash \
  -data $workspace -consolelog -clean \
  -application org.eclipse.equinox.p2.director.app.application \
  -metadataRepository http://download.eclipse.org/releases/ganymede \
  -artifactRepository http://download.eclipse.org/releases/ganymede \
  -installIU ${installTargetFeatureGroup} \
  -destination $eclipseroot \
  -bundlepool $bundlepoolDir \
  -profile ${installTargetFeatureGroup}.profile \
  -profileProperties org.eclipse.update.install.features=true \
  -p2.os linux -p2.ws gtk -p2.arch x86 \
  -vmargs \
    -Declipse.p2.data.area=$eclipseroot/eclipse/p2 \
    -Xms128M -Xmx256M -XX:PermSize=128M -XX:MaxPermSize=256M 
echo "Installed sizes: "; du -shc $eclipseroot/eclipse $bundlepoolDir

echo "";
echo -n "[`date +%H:%M:%S`] Starting Eclipse workbench (to verify installation) ...";
#  -console -noexit -debug
./eclipse/eclipse -vm $vm \
  -data $workspace -consolelog -clean \
  -vmargs \
    -Xms128M -Xmx256M -XX:PermSize=128M -XX:MaxPermSize=256M 

popd >/dev/null
echo " done."

If you need to translate this to Windows command syntax or wrap it with an Ant script, see Starting Eclipse Commandline With Equinox Launcher.