hello i enjoyed dawnguard very much but one thing occured to me i never fought one of those frost giant things when i was joined with the dawnguard, so is it for a quest for the vamps or what?

No, the Frost Giants are scattered throughout the Forgotten Vale.

There are 5 frost giants and they have paragon gems on them. There is a portal in the vale to activate with the gems and you can go to a different small area that has a treasure. The ruby paragon is the best. There is a thread out of extreme detail on where to find each one. Paragon location I think is what it is called.