For most internet videos to stream correctly, then faster your internet connection, the better.. If you're on dial-up, forget it.. If you're on a budget DSL running, 750 Kbps download speed, it won't stream well without a great deal of buffering.

That said, even if you've got a fairly decent 1.5 Mbps or better connection, you need to confirm exactly what you're getting. Have you done a bandwidth speed test? There are a lot of site available which will give you a fair baseline for determining what your speed it.. Just a couple of examples below:

I use the Java test in the one below:
http://www.dslreports.com/stest

or

http://pcpitstop.com/internet/Bandwidth.asp

Hope this helps.

Grif