Choosing a format : parameters to take into account
Don't use a new media because it is new : chose it reluctantly because you
really need it, and make sure that your web site is still usable without an
access to that latest trendy next-internet-revolution...
Did I already told you that all the computer are different on the net ?
Display Size : From 640x480 to 1600x1200 pixels
Processor speed (important to decompress video or java animation)
Video System (integration of multiple video, 3D)
Browser type and settings
Network Configurations and Firewalls