goto: Grid button on your mini map , click on the status tab , click on the Auras option in the drop down, fill in the name of the buff /debuff in the required fields- and test it out to make sure it works correctly.
you can also get support packages on most any add on website that is called GridRaidStatus : Cataclysm that should already have this option in it, if not just follow the above steps and you will be good to go .
In the status tab you should be able to add buff and debuffs, and then you can go and add where you want it to show in the indicators tab.
Say you add "buff: PW: Shield" and you go to the indicator tab, down to middle icon and wing off the "pw: shield" and you will have PW: shield showing as middle icon, work out the rest yourself
EDIT: #2 beat me to it! But now there should be no doubt on how to do it.
Last edited by mmoca9f8cb92b6; 2011-03-04 at 09:14 PM.