what resolution for 450d?

I'm traveling for a few months with my new 450d w/ 17-85 lens. However I was surprised by how quickly my 8gb memory card is filling up. I'm thinking that 12.2MP probably isn't very useful for me. don't know much about sensors and lenses. How much should I reduce the MP without losing image quality if I'm viewing on a camputer or printing up to say an 8x10. I know that MP aren't everything and that increasing MP doesn't always have a possitive effect on image quality.