Thanks Jim - I checked by unplugging the power supply and the screen does dim considerably (making it even worse) but I usually work with wall power anyway so I guess it just one of those things I will have to put up with.
I am sure spending more money would have got me a better screen, but I had a figure in mind and spent several weeks getting specs etc to make sure I got the best deal for my money. I thought 64MB graphics would mean a pretty good display but I guess it's down the actual screen they use!
Anyway - thanks for all your replies and suggestions!