How to map a page in the header to point to a different site

Hi I want to modify the page to point to another website on the network.Please Suggest

I am running Buddypress on a multisite network http://morningtadka.com .I have installed the Social theme on the site and have created another sub domain i.e shop.morningtadka.com and i want a link in the header to point to this sub domain i.e shop.morningtadka.com.Please suggest how i can do this Asap.

regards,
Joel