color variations between vista and xp

Greetings :)+

I do some graphical work for a person to make cutter files for them to make horse stall curtains. They usualy want a visual sent in a jpg format to approve. I was using Corel draw for my work on an xp. One day CimonesUnlimited (the stall curtian maker) got an email back from their client asking why the colors were not what they asked for. CimonesUnlimited did not know. For what I had sent them looked good on their computer also as well as mine. CimonesUnlimited was also using an xp. So I decided to send my file to one of my other Vista computers and it indeed did not show the right colors. Now I switched everything over to the vista and bought a new corel draw for vista and there is still the same problem now if I send from my vista to an xp the colors are way off. It acts like the jpg colors are different for the different operating systems? How can this be, and can anything be done? Not every jpg has differences so maybe it is a corel problem, and I may need to comtact them? Any suggestions?
Thank you,