The very best/easiest way to do this event (especially if you like to do things with only a couple groups) is to keep your raid to the left of the entrance to the room (along with your banner),move enough people up to the boss to pop the event then all but 1 kiter (sk is best) move back to the raid..kite the zombies while warriors pull off 1 at a time and take them to your raid,beat them down to around 10% health (make sure your pallys get off early to avoid accidental kills) then mez them...once all are mezzed and low start killing them off...after successfully completing this part of the raid your raidforce will be set up in 2 columns..at this point you want to move everyone back to that corner quickly and have a wizzy AE TL your raidforce out to their binds (lol...yes i actually DID say AE TL muahahaha)...only 2 people stay behind-mnk + bard or 2 mnks (bards + mnks because they have run7/8..without that they'll take hits and eventually die trying to kite them)..the bard (or one of the mnks) will pick up all of the giants and kite them in the back* of the room-the second mnk is there just in case the first gets stunned and goes down..the reason for this is so that no one else from your raid force has aggro on the 4 giants (and will not pick up aggro for healing tanks fighting the other giants).
After your raid has bannered back in (you did set that banner...right?) have an SK tag the giants off of your kiter 1 by 1 until you get them all down (and FD while the others kill it to avoid cross-aggro from the other giants)...at around 10% health on the last giant you want to have a strong sk/warrior head to the back of the room where the boss spawns and pick up/kite him while the raidforce runs to the *back corner* (furthest from the entrance on the right) of the room near where he spawns...reason being that when the giants you just killed are revived by the boss they'll respawn where you killed them...so since you're all the way across this very big room they'll respawn and not aggro~. Hopefully you have distributed your healers pretty evenly because grenwald has a very nasty AoE-groups will die without heals. Make sure that when you move back to grenwald you set your banner back there so that no knuckleheads can banner in,aggro the revived giants and train your raid.
too easy~