Well, I watched yesterday's game when Piazza tripped over the bag at first and went flying. By the looks of it, his injury is not severe. He walked off the field on his own without a problem and was laughing and joking about it in the dugout. He may well have been pulled for a pinch runner in that situation anyway.
Giles' injury has the potential to be a real nightmare. He is having more tests run on his knee and the Pirates are supposed to make an announcement tonight. If the tear is not signifigant, he could well be back in two weeks. If it is a substantial tear, it will likely be 6 weeks. And, if it requires surgery, he is gone for the season.
Durham will probably only miss a few games with the groin injury and isn't likely going on the DL. However, the problem with him is that his primary value is as a base stealer and if a nagging groin injury prevents him from doing it, he isn't much use to your team. Since Durham is not a great average or power hitter, if he can't run well, he might wind up losing playing time as well so this could be a major concern. I would pickup a backup 2B if you don't already have one. D'Angelo Jiminez is a great option if still on waivers.