there was no iBook G3 800 MHz machine... at least none that I can find in the iBook G3 series list... anyway, presuming you are using a G3 machine, that debuted in 1998... 8 years ago.
I'd say that between your RAM (640 meg) and OS and CPU and iTunes, running choppy iTunes video would be expected... And I would not expect QuickTime to play iTunes video as that would probably defeat the security required by the studios and artists... But 8 years is a darned good run!
As for the sleep issue - I suggest you check out the Support area at Apple.com. The Knowledge base and user forums are quite extensive.
I have an iBook 800 Mhz G3 640 MB SDRAM OS 10.4.8
If I try to view a video purchased at the Music store or a video podcast, the playback is choppy both audio and video like its buffering.
Is the reason its doing this because of the G3 processor or what?
Can Quicktime play iTune videos?
I've never had a problem with QT playing a video however I don't see an option on the iTune preferences for video playback with anything other than iTunes.
Also, half the time after I close the lid, I get no desktop after reopening and am forced to power up without shutting down properly.
Is this a sign of something not kosher? Thanks.