An unsecured laptop is a safety liability in the air, the hard drive will almost certainly pack up at altitude anyhow (most rely on air bearings and even well mounted in research aircraft pack up at about 8000ft density altitue, although solid state netbooks are good).
A cheap HD camcorder will provide far better quality than a webcam, and cost about £65 on eBay or Amazon. Or just mount a standard digital camera on a cheap mount and use that - most people have something suitable already.
G