Full screen video choppy?

Whenever I watch some videos full screen (Over the net) it becomes choppy. I.e. youtube, collegehumor, break, etc..

When I watch videos on Netflix full screen, they are fine.

When I change the Screen Resolution from 1440x900 (which is recommended and what I like to keep it at) to 1290x800 it'll run fine.

I bought the computer off of my brother, and upgraded the ram to install windows 7.. Heres what I know the computer has,

ASRock 775DUAL-VSTA Motherboard
Nvidia 8600GT Vid Card
2 Gigs ram
Intel Core 2 4300@1.8 GHz (He said its overclocked to 2 GHz.)

So my question is, why does it run so choppy at a higher resolution, but at a lower resolution it runs fine?

Any other questions about the computer let me know and i'll find out. Thanks in advance.

Are you talking about in Media Center or just in general? Does it do this in a browser or a certain 3rd poarty plugin for Media Center?

Happens in just the browser (Firefox, chrome and IE8). Watching a DVD is fine.

Check for the latest Adobe Flash Player.

I've got that. I re-downloaded it to be safe. Videos are still choppy.

I know more about computers than your average user, and can usually solve minor things on my own, but this one is boggling me. My little bro, who built the computer, has no idea why its doing this either.

Make a test. Download a YouTube video that performs choppy when on-lne (you put OK between WWW. and YouTube and hit enter) and see how that plays once it is on your machine. If that works OK, it can only be the browser, (Adobe) or your DSL. Then we would be a little closer to the culprit.

For the most part, everything is fine now.

I'm still experiencing trouble with theofficefree.com going full screen at a higher resolution. But It may just be on the websites end.. I think it should be fine now.

Usually I use for screen video there is Screen VidShot.