I've fished Pend O'Reille a bit...knocked the paint off of many lures there. In addition to Kamloops Trout, they also have a good sized population of Mackinaw. For the Kams, you'll need either downriggers or planer boards (I like the new Sidewinder boards. They're small, easy to use and effective). There are several good fly patterns designed for the Kams. I've had the best luck trolling for Kams when there's a pretty good chop on the lake.
For the Macs, I fish around the islands located at the north end of the lake but others do well in different parts of the lake. Macs tend to stay right on the bottom, but I have found them suspended in Pend O'Reille at times. You will definitely need downriggers if you plan to troll for Macs. If you don't have downriggers, you can dropshot them (jigging) but I've had better luck trolling. Pend O'Reille is a big beautiful lake...just pay attention to the weather reports. Storms tend to move in quickly and you can get yourself in trouble if you're not careful.