Video 'stuttering'

Just bought my son a new Dell Inspiron 1525 laptop. Whenever He tries to play Videos on Youtube or Googlevideo the video stutters badly. If he pauses it and allows it to download fully it plays fine.
He's running Vista Home Premium with 2 Gb Ram.
Intel® Core™ 2 Duo Processor T5800 2.0 GHz.
Integrated Intel® Graphic Media Accelerator X3100.
I dont think its a bandwidth problem with my ISP because we have 3 other Pc's in the house anf they all play videos fine. We've also downloaded the latest version of the Flash-player. He's a teenage lad so as you can imagine he spends a lot of time on Youtube so this problem is driving him bonkers :) The PC is only 3 months old.