[2DAXTRM (Jeff)]

First of all, I would not have bet 300 on the flop. I prefer checking and folding to a lot of action. If you really want to play for the pot just move all in although I tend not to do this.
On the turn I would probably check and fold. The best case situation at this point is that one person on a diamond draw, and the other has 99 or a smaller pair. This is not a very fun situation and that's why I never bet $300 with a medium sized pair with no overcards on the flop.