I agree, the problem was specific to the laptop, or more precisely, specific to the combination of laptop hardware, vista, and zenfolio. Every other hardware/software factor (browser, laptop hardware, wireless network) I can rule out. The problem was there with both firefox and ie, and both of those browsers worked fine on all other machines on my network. Also, the laptop in question worked perfectly on every other website I would visit (image intensive or otherwise).
Anyway, I'm happy now. Don't mean to prolong the topic, I'd just love to know what fixed it, in case the problem ever surfaces again.
Art