how do i find all the files in one folder that aren't in another?

[bigdan]

I'm unzipping a huge amount of files right now and this has taken hours. Who knew unzipping takes so much processing power.

Is there a way I can see all the files that are now in one folder (and it's subfolders) that aren't in another folder hierarchy? Essentially I want to copy certain folders in my C and H drives.