Pete,
You've discovered the need for colour management

It's not a simple subject but the basics are that you should calibrate the screen you process with, process in a colour space that suits the screen and your needs (sRGB is good if you don't have an expensive wide-gamut monitor and mostly want to make images to display on the web) and make sure that your images files are written out including an ICC colour profile. Oh, and you should make sure that you view your images in a program that does colour management and has it turned on.
Here's a little reading to get you started:
http://www.cambridgeincolour.com/tut...alibration.htm
Cheers,
Rick.