Our floor is particle board (I'm pretty sure that's what it is called) and our house built 1979. We have 4ft x 2 x 2 tank in the lounge no problem. It is also surrounded by a wall to wall, floor to ceiling bookcase full of heavy books. If I remember correctly we have an extra pile underneath though as originally the fireplace was going to go there.
If it against a load bearing wall with the floor joists running at right angles to the tank length it should be fine.
Think of it this way, if you had Greg Somerville (115kg - thanks to the Weetbix packet I know this), and 3 or 4 of his equally large mates visit, would you tell them they couldn't all sit together cos their weight might collapse the floor?