Hi Calendril!

Check out this thread: http://www.cartographersguild.com/viewtopic.php?t=63

Something else you might try (although I've never tried it myself, so I'm not sure how well it would work) is to import a snapshot of some terrain from Google Earth into a paint program like ps or gimp and then warp it roughly fit your continents and use that as a guide.

All the best

Ravs