Hi-
You should get better than 1 fps, there is no question about that.
But, issues from net provider/bandwidth, to the software and hardware in use all play important roles in video playback.
HD is a problem in and of itself.
So is Flash 10x.
Neither is going to run on a G4 optimally, whatever you do.
Multitasking, or having multiple software open during viewing, is also a problem.
Heck, even Safari, alone, can eat up 70%+ of a processors power, leaving little for video.
Macs (OS X) use roughly 5x more CPU to run video than WinPC.
Even with plenty of GPU (graphics card) which the Radeon 9000 is not, the CPU will always be overloaded trying to produce that which it's architecture, is not optimized to do.
Not saying that a new, powerful graphics card couldn't help, as it would, but the issues surrounding net video are more complicated than a simple upgrade.
If web software provided broader support, one might have a chance.
But, since HD is a technology that is way newer than G4 technology, it is one thing that will never run "just right", simply due to lack of optimization on the part of the providers/hosts.
Add to this, that not all video formats, nor encoding softwares are created equal, and you have a real basket full of vipers to contend with.
Youtube software is also not optimal.
Recent "upgrades" or "enhancements" seem to have worsened the problem.
Other sites are infamous for poor playback.
I know I am not the only one that has problems with CNN........
Complicating the issue is bandwidth, which most iNet providers still scrimp on/overbook.
But, even with a fiber optic net connection, HD requires newer hardware......
These are the requirements for HD at 24 fps in QT:
http://www.apple.com/quicktime/guide/hd/recommendations.html
I believe these are WAY understated.....
Besides, one needs 40 fps to have playback that is not "jerky" to the human eye.
One may consider different video handling software.
I see better playback characteristics with VLC.
A newer hard drive with lots of free space also helps.
Look at this for other optimizing techniques:
http://www.thexlab.com/faqs/performance.html