Jumpy Videos

[janz101z]

Hi just wondered if anyone could help, Im pretty new to mac's I have been given a G4 and when I try to watch any videos on the internet , they are very jumpy, it is almost like stop start, it cetainly isnt flowing properly, would I have to clear something on my system to get it to view better, it has an 867 MHZ processor and 1.5 GB sdram
The operating system is Mac osx 10.4.11. I have downloaed the lastest version of flash and shockwave to see if that makes a difference too.

Thanks.