This could be several things....
1) make sure your IDE drive isn't in PIO mode vs. DMA.
You can check this in control panel ->system ->hardware -> device manager -> IDE ATA/ATAPI controllers
Check all of the channels for their "transfer mode". You want them to be in DMA mode.
2) Bad codec
Have you installed any strange codec's on your desktop pc? Could be a decocding error.
You didn't mention the specs of these machines.
4) try another viewer.
If you have powerdvd winddvd or ndvd, try playing the mpg's using these programs. They have their own graphedit codec's and will ignore whatever your computer has as default.
5) burn to cdrom
If it plays from the cdrom, there is an issue with your drive, althogh I would be very surprised by this.
6) check WM9 settings
Do you have "video smoothing on?" this and other options will effect mpeg playback.
in WM9, go to tools -> options -> performance -> advanced
If you can choose "hardware" decoder, do it. uncheck "use video smoothing" You can also play ith the video mixing options