Laptops work well up to about 4000 metres/13,000 feet. Altitude can destroy or wipe hard drives bigger than 7 - 10 GB above this altitude, or hard drives that have a moving disk. There are several options out on the market for non moving hard drives that work well in altitude. Panasonic make a special laptop called a "Toughbook"; it is expensive, but we once chipped one out of the ice in a tent at 7500 metres and it still worked.
Note: Some early ipod and mp3 players have this problem as well. Check to make sure your ipod does not have a moving drive, especially before you turn it on above 4000 metres. We have had several instances where these were wiped or crashed. Digital cameras work well. We recommend that you keep them in your jacket during the day and in your sleeping bag at night.