Devs said it should run fine on systems that are a few yrs old.
The one you linked is fine for medium settings IMO. I don't like the CPU or GPU very much, and if you are buying a separate GPU then you have to make sure it's compatible with that power supply.
The key to MMO's is processor. The graphics won't be demanding, but the amount of players will require a good CPU if you want to run smoothly in big battles.
The core i5/i7 series have been pretty dominant in the market. I know AMD has some cheap 6 cores, but at this stage no one knows is PS2 will support more than 6 cores.
I would advise building your own system if you have time.
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