Bitcoins are only generated every 10 minutes (on average), so it would probably not be worth it for a company to dedicate a huge cluster of computers to it. At most they could earn 50 BTC/10 minutes, no matter how much computing power they'd throw at it.

It get's more interesting if a company could calculate blocks faster than all the other nodes combined. Then that company could forge the complete chain of transactions.

I think there are even numbers floating around in the BitCoin forums as to how much it would cost to build such a server farm atm. So yeah - with enough money you could ruin BitCoin, but why would you be motivated to do so? Also, it gets harder every day, as the network of nodes grows.