Differential File Copy by Date?

In final preparation for copying back all my data from my backup drive, I have one final question before I proceed: I have my backup data and programs of my external USB drive. My current working copy of Vista has some recent files on it; I have a secondary backup of what was my original Vista drive in the directory Vista nicely saved for me in "Windows.old".

Now what I what to do before I copy my backup partition over my current working partition is to first copy files onto my backup partition from Windows.old that are newer than that which is there, then copy all files that are newer from my working partition, and then I can comfortably copy my "enhanced" backup partition on top of my current working partition then reboot and lose virtually nothing.

Does anybody know of a utility -- preferably free -- that will compare two directories and their sub directories, and copy to a target all me those files that are newer?

Thanks!

Ross