Yes. Very easy. 15-20 minute walk. Disneyland usually opens at 8am. If you leave the hotel at 7:30 you will get an early start before the crowds. Walk straight on to Space Mountain or Matterhorn.
Insider Tip: from the HP, if you walk across Harbor and into the parking lot, I think you can get on the shuttle to Disney. They think that you parked your car in the lot and have no way to verify. It's worth a try. As always, YMMV.