Lasseter,
Please tell us how you connect to the Internet (Dial-up modem, Cable, DSL, etc) and the estimated speed of your connection. Google "modem speed test" and try several to make sure your connection is not at fault.
Next I would try downloading 100% of the movie clip, then viewing. If it's still balks, you may have your resolution set too high or the graphics card could be choking. Please post your video hardware and monitor specs.
Tony
"...an eye for an eye leaves everybody blind" - M.L. King