I don't think it will be the death star (I don't think this will come into play until E3). I would say it could be an early version of a star destroyer. This is because, the Old Republic was peaceful and had no need for that type of destructive technology. However, they were plentiful in the OT. Things like that don't appear overnight and as with our war technology, we need "prototypes". Palpy probably had this prototype constructed without the senate knowing.
But I could be wrong and it could be an early death star laser. But in ANH when all of the top brass where discussing the death star it appeared that it was only just fully operational and was yet to be tested (enter Alderaan).
I'm just saying that the new weapon better not be a super laser like on the Death Star. I watched ANH last night, and I paid attention to all the Death Star scenes in particular. The idea of a planet destroying weapon was Tarkin's idea to go with the plan of ruling by the threat of force. Destroy one planet and you'll never have to destroy another one again. The construction of the super laser 25 years before ANH seems like too much of a stretch to me.
Perhaps they had it planned as an enormous millenium-celebrating garden centre, before the Empire changed the plans...
The most terrible, terrible possibility is that it is a prototype superlaser, used to wipe out the Jedi in the Temple in one stroke. I'm far more comfortable with the Victory-Class Star Destroyer idea.
The superlaser/bomb thoery has been advanced in the past as an attempt to work ouy exactly HOW 10,000 of the hardest people in the Universe were ever tracked down and killed- destroying the Council would seem almost impossible. The possiblity of some Sidious uber-force thing still exists...
My bet is still that wewon't see the Jedi wiped out in the Prequels, just the events preceeding it... so we have to foucs more on how they kill the Council. A super-weapon just seems such a poor way of doing it...
According to rumours only a four members of the 12 council memebrs survive Ep2. I guess that means some slaughter take place. There's supposed to be a big fight in the arena where Jedi fight super battle droids. I'm sure a couple will die. So I'm not so sure about that.
As for the superlaser, it would not be the major tool for destroying ALL the Jedi. Vader helped hunt down and destroy the Jedi since a laser would not be able to wipe them all out. And the true power of Palpy lies not in the hardware but in his power in the Dark Side. So I'm sure to efefctively kill off the remaining Jedi Palpy needs the best to do that.
Also, if you want to develop a super laser that can destroy an entire planet you need to first develop the idea, prototype. Second, you need to develop some kind of ship taht can carry it. Maybe there's a SD in amaking with a smaller version of it. All in all, making a Death Star like that may take many many years. But it's just a thought.