[THIS HAVE BEEN FIXED. So it doesn't work anymore with PTR client or the beta client.
Hello! I will now tell you how you can load the Cataclysm areas if you downloaded the PTR client.
As you know with the PTR client all the Cataclysm areas are disabled. But by deleting / moving the base-enGB.mpq (Dunno if it's another name for other clients) out of the "World of Warcraft Public Test\Data\enGB" folder you will be able to load the revamped areas.
Video: YouTube - How to (kinda) play Cataclysm NOT Sandbox
Thanks to Leonim for making it.
Important notice:
I'm NOT sure if this works with all clients, I've only tested it on enGB.
It seem like this works for some people and not for some others, not sure what's up with that.
This will NOT load new quests(Atleast what I know of).
You will see all the old npc's and people floating around in the air at some places where the height have changed.
Zones in Kalimdor will probably give you and error on load(Does for me atleast).
I'm not 100% sure if all zones are loading correctly (See above).
You will not be able to play the new races OR use the new class / race combinations.
It seem like flightpaths and chatting don't work when you are using this.
The old fatigue zones still apply so watch out where you going so you don't die due to that.
Last but not least, use at your own risk seens I'm not sure it it's actully bannable to do this.