A few suggestions..
Make sure no other programs are running during these sessions--that would include programs that run in the background as indicated by little icons in the bottom right of the Windows task bar.
Try disconnecting from the network.
Do your machines have good graphics cards? Or do they have integrated graphics processing on the mother board? Do you have the latest drivers?
Is video acceleration turned on (if the option is available in your display settings)?
If your monitor is listed as a generic plug and play monitor, you might try installing the driver for the actual make and model.
Would be curious to know if any of these ideas work for you!
see also: http://www.empirisoft.com/support/showthread.php?t=625