dreamweaver courses - Pixelation and viewability problems

Hi All,
I have had a few people comment that our website http://www.kme.co.uk on occasion doesn't load up properly and I can't figure out why as I can't reproduce the problem. On most peoples web browser there is no issue and the images load without problem but I have been informed by 2 separate people that the picture I have on the front page comes up as a blue blur and the following pages do not load correctly either. Initially my theory was that it could be something to do with the versions of Internet Explorer they used (I create the website in IE7 in Dreamweaver and they were using IE6) but having tested a few machines this doesnt seem to be the case so now I think it could be something to do with their graphics cards?
Apparently ours isn't the only website that this occurs on but that is all the information I have which as you can see is posing a bit of a problem! My personal opinion is that it is something to do with their machines but is there anything I should be doing to combat the problem? I know about changing the default browser in Dreamweaver for other applications such as Firefox, but I dont think this is the problem.
Have you got any suggestions?
Hope you can shed a bit of light on this...
Jo Stephens.