Abhi,
We do not provide intrinsic support for third party plugins, but we will try to assist you in this case.
Go to MyEclipse Configuration Center > Software > Add Site > Enter the below URL and follow the wizard.
http://releases.liferay.com/tools/ide/eclipse/indigo/stable/
Alternatively, Go to MyEclipse Configuration Center > Software > Add Site > Add from Archive, select the downloaded Liferay archived update site file and follow the wizard.
You can download the “Liferay” archived update site from here : http://sourceforge.net/projects/lportal/files/Liferay%20IDE/1.4.0/liferay-ide-eclipse-updatesite-1.4.0.zip/download
Here is a detailed tutorial on how to add the plugins to MyEclipse :
http://www.genuitec.com/blog/?p=1628#add-site
Let us know how it works for you.