[QUOTE=darth_daniel]Was Malachor originally a normal planet with people living there or was it always abandoned and such a horrible place?[/QUOTE]
Malachor has always been a source of dark side energy, so, yes, it is safe to say that Malachor has always been an unpleasant place. There is no mention in the game or the canon (such as it is) about it being inhabited before the Mandalorian wars. The Academy may have been constructed by Revan, or it may have been a relic of the True Sith; the game and the canon can't seem to agree. If you can put up with the inconsistancies/ contradictions and fancy a read, you could always check out the chronicles,
here . Not too reliable, but it passes a few minutes in an agreeable way.
[QUOTE=darth_daniel]And at the end of the game, does Malachor implode? It seems as if it was breaking in 3 big pieces or something like that and all the damaged ship parts sucked into it. That right?

[/QUOTE]
Explosion/ Implosion... You're not the only one confused. Whatever the MSG did to Malachor when it was first activated it caused the ships in orbit to crash, but did not end its influence there. Re-activating the MSG destroys Malachor ending the famous "echo". Wikipedia is equally confused, but you can read their contribution
here .
[QUOTE=darth_daniel]Oh and, what did you mean there isn´t much T3 can tell me cause I´ll find out? Do you mean he doesn´t know more than what Kreia tells me at the end?[/QUOTE]
T3 carries a message (either from Carth or Bastilla depending upon whether you said Revan was LS/DS Male/Female when you spoke to Atton at the beginning in the force cage). The message itself isn't important; the person who left it knows that he/ she is about to be left behind and wants to make sure that T3 will keep Revan safe. T3 also travelled with Revan and brought the Hawk back, either because Revan sent him back or because Carth/ Bastilla told him to come back and find help if it all went sideways. Either way, he can't tell you much more because, after the Navicomputer was locked, he wiped his memory.