Can I relocate scenery files to a different hard drive?

I have just upgraded to a new computer, and have reinstalled FSX after being away from it for a long time. I have a number of MegaScenery packages, and I’d like to install them on an external hard drive. I vaguely remember that there’s a way to do this so that FSX will find and use them. Can you give me this procedure?

Thanks,

Barney Bornn