Printer is several years old and has always performed properly until recently.
I have tried under windows XP and win 7 and also on a new laptop and using different photo papers always get green tinged photos!
I've used Canon's Easy Photoprint and also Photoshop CS3 - same green results but perfect on plain paper - it beats me!
I hope somebody can enlighten me- help!!

Are you using original Canon ink, or noname?
If you are using noname ink it most likely is the cause. Noname ink is of cheaper quallity and black is not real black but a very dark green.
Another problem with noname ink is that it is chemically aggressive and destroyes the printhead. So it might happen that you invest your money into expensive Canon cartridges and the result will be the same.
Maybe you should save the money for the cartridges and invest it into a new printer, and keep using the original ink.
There are good printers with affordable original cartridges (Brother e.g.)
But before: did you try to calibrate the printheads? (Should be an option in the Driver-Settings)