You can install the plugin using the Eclipse Update Manager:
Help > Install new Software
Work with: http://hge.javaforge.com/hgeclipse
[ Add... ]
[ OK ]
check HqEclipse
[ Next > ]
[ Next > ]
check "I accept the terms of the license agreement"
[ Finish ]
confirm Security Warnings dialog with [ OK ]
Restart your Eclipse
https://j2m.googlecode.com/hg/
https://hgeclipse-demo.googlecode.com/hg/