Within the last few weeks, my laptop has begun to experience constant pauses whenever I am trying to watch a video stream (YouTube, etc).

The system is about 15 months old, and it did not exhibit this syndrome until now, Core2 Duo, 2.0Ghz processor, 2GB RAM.
Windows Vista Business, SP1 has not been installed, but all suggested updates have been applied.
No other software has been installed recently.

As a comparison, audio-only streaming is not affected at all - last week I streamed and recorded a 3 hour performance from Radio RAI-3 without any interruption whatsoever. Further, there are no problems playing standard video (DVDs and Real and Windows Media files saved on the hard drive).

Thanks as always for any ideas as to what might be causing this.

Streaming video is a bandwidth-intensive application. Do your other computers using the same network connection have this issue? It might be caused by other traffic on your connection, other traffic in your network neighborhood (neighbors' bandwidth-hogging computers sharing the provider's network node) or bandwidth-throttling by your Internet provider.

I have this problem but believe that in my case it's on my provider's end, possibly due to network congestion, because it happens in the evening but not in the early morning and is not site-dependent.

It's extremely frustrating.

Also agree that it's probably bandwidth, but I'd also suggest trying to set the power management to "Always On" and see if that fixes it. If it does, Windows' power management isn't ramping up to meet the needs of the computer. Vista does some strange & stupid things with power management and network traffic w/regard to multimedia.

Good suggestion. In addition to that, disable background programs and service you don't need. Turn off the sidebar too.

yup, definitely disable background services (msconfig can help with that).

Also, check with your provider--it could be that they're having problems. I've had a lot of issues with streaming during the Olympics, for example, and I know Comcast had probs in my area...

Are you connecting wirelessly from your laptop? If so, maybe you have some issues with your wireless connection. When you see the problem happening, disable the wireless connection and plug your laptop into the router to see if the problem goes away. If it does, the wireless connection is the problem (which can be remedied).