In a perfect world your HD will be more than enough for you, but we all know how that goes. I know this one personally...had a 80gb drive go kaput.
What you should do to protect yourself is to have the photos on a backup drive, independent of your working folder to ensure you dont accidentally alter the photo from it's original state. As well as DVDs in one or two locations.
As soon as you can you should always back that same data up on DVDs. Gold Standard DVDs is where you need to put them. They have a 100 year shelf life. You should keep backups on two separate locations. Never keep all backups in the same locations ie your home computer, DVDs in the closet. Should a catastrope happen to the one location, youre screwed.
What I do is I have one central external harddrive (500 GB) for all my photos. It doesnt move, but should I need, I can unplug and walk away with it in under 30 seconds. I backup on DVDs. I have my working photos on the computer harddrive. For all my Digital Family photos I have them backed up on DVDs and placed into the safe. I have no idea if they would survive a fire inside the safe but they will do better than on a desk. I need to keep DVDs in a drawer at work (locked) but have not gotten that far. "mom's house" would be my second thought for off location.
Hope this helps
A good photograph is knowing where to stand.
Ansel Adams