Give all that others have said, here are 3 things that might also help:
1) From Cnet.com you can download a trial version of TuneUp Utilities 2011. I believe they give you full access to this great software free for 14 days or so. If it doesn't work for you, just uninstall it. I've used it since 2006, to cleanup my registry, delete temp files, correct computer problems, defrag my hard drives, and much, much more.
So, why would you want to try this?? One of the great features of this software is that it can optimize your Internet connection to the type of service you are connected to. Here are the choices offered during setup: DSL, TV cable or power line; fiber optics; cellular; satellite; dialup connection from landline; other connection types. I have mine set to "From 25 Mbit/s DSL, TV Cable or power line" Internet. The DSL, TV Cable or power line setting alone offers these choices: "From 1, 2, 3, 6, 16, 25, 50, and 100 Mbit/s." As stated, my access from Comcast is at 25 Mbit/s or higher.
Once the proper choice is made, TuneUp Utilities will optimize your Internet connection for the general speed you receive from your ISP. This can improve download speeds, at least at with your computer.
2) Reset your modem by disconnecting it and waiting 30 seconds or longer. Then reconnect and wait for Internet connection to show again. Sometimes one may have to disconnect both the modem and the router to get a new dynamic IP address, one that doesn't have the load on it of the one prior. (This is a technique I often use to get my bandwidth up again to were it should be. Too, Bandwidth can fluctuate depending on customer demand and other Internet issues.) When both modem and router are disconnected, reconnect the cable modem first and wait for Internet to show, then reconnect the router, again waiting for it to show an active connection. Then try streaming.
3) Try a dedicated streaming media device, such as a Roku (models HD, XD, or XDS). This media player can stream in HD for content provided in that format, but also just does a better job than both the Xbox 360 or Wii at streaming SD content. This should work better than a direct connection to an HDTV too, though I haven't tried it. My choice was the Roku XD streaming player after I used my Wii for awhile. The Roku does a much better job of streaming media than my Wii every did, besides I can get several other streaming services not available on my Wii (Amazon Video and Hulu Plus and others).
Slow downs still happen where a movie must reload, but this doesn't happen often and when it does I can tell Netflix to "retry" and it reloads within a minute or so. My Amazon and Hulu Plus services just freeze on screen but will startup again in a moment or so. If they don't, I just restart my Roku player by unplugging and replugging (there is no on/off switch), and once it reboots I can get back to my movie again within minutes without problem.
My setup: Host computer - Win Vista Ultimate x64, 6GB RAM connected to Comcast cable via cable modem at 25+Mbps connected to a Netgear N600 Wirless Dual Band Gigabit Router with 1000m ethernet, connected to Roku XD Streaming Media player, connected via HDMI cable to Samsung 40" 1080p HDTV. Internet is optimized with TuneUp Utilities 2011 and my network is controlled with Cisco Network Magic Pro.