I can't help you PentUp, but I can disprove some of what all the websites are saying;
You do not need to kill rifts of your own level to get the "Tripping the Rifts" achievement.
If this isn't intended, I can imagine it getting a hotfix, but I just got the achievement at 11/02/10 (that's 02/11/2010 for you Americanos) around 1 'o clock by killing only Outlands-based rifts.
Outlands seems to be the best place to get this Feat of Strength - you can teleport to Shattrath, fly to Terrokar for Air, Zangarmarsh for Water and Nagrand for Earth. The only real amount of effort involved is when you have to fly all the way over to Hellfire to get Fire. Since the portals spawn once per hour, just wait until the correct time before setting off to Terrokar (for me all portals spawned around 00:50), after which you should be able to get all elements in one go.
The quests to actually kill these rifts don't seem to be active yet, but I can pretty much confirm that you will most likely need to kill rifts of your own level to do these. From what I've seen the rifts are supposed to turn into devices required for these quests - they did so in Outlands, but I couldn't in any way interact with these devices.