Did you install Flash 10.1 Public release on an older system and now flash video plays even worse? Yeah, I put it on my old AMD Athlon 3600 single core XP box with an old GF 5600 4x AGP card and it is lag-0-ramma! 
So, I used the Flash Remover Tool for Windows and then installed Flash 10.0.45.2 and the old GF 5600 is liking flash once again. Still pegged at 100% cpu, but it’s fairly smooth again. 
Well, in case you’ve never seen it, Adobe has an Archive page for all their flash releases for use on older legacy systems for when things go a touch wrong. They break it down by series number: 10,9,8, etc. If you select Flash 10, you will get a zip file that has every public release of 10-10.1. Each will have Windows ActivX (for IE) & Plug-In (for netscape and FFox), Solaris, Mac and Linux.
Anyway, here are the links.
Flash Archives:
http://kb2.adobe.com/cps/142/tn_14266.html
Flash Uninstaller tools:
http://kb2.adobe.com/cps/141/tn_14157.html
About Flash-Tells you which version of flash you are running on that particular browser.
http://www.adobe.com/software/flash/about/
