The problem most likely has to do how the Slingplayer interacts with the Windows XP's graphics subsystem. I would recommend testing each of the settings to alter the Video Mixing Renderer support.
This can be manipulated in Slingplayer Options | Video tab | in the Optimizations subsection. There are two scheckboxes. It can be toggled all off for Legacy (GDI), one box checked for VMR-7 (DirectDraw), or both checked for VMR-9 (Direct3D). Make sure to close the Slingplayer after making an selection, and then make sure it is selected after you restart it by pressing [Alt]+[Shift]+[i]. You'll see a statistics window where you can verify the current rendering mode of the Slingplayer.
Unfortunately, if that doesn't resolve the problem then you'll have to make sure his graphic drivers are up to date along with all the Windows Operating system files especially the ones that concern DirectX.