Can my PC play HD stuff?

Any graphics card will play HD resolutions, although higher end cards will do it better than lower end cards. Yes, you need an HD capable monitor. If you were to download HD content straight to your computer, then you would need only that. However, if you want to play HD or Blu-ray content from a disk, then you would need either an HD DVD or Blu-ray drive. Keep in mind that HD DVD drives can't play Blu-ray disks, and Blu-ray drives can't play HD DVD disks.