DirMerge

This program can be used to copy one folder to another with a number of extra options that you don't have in Windows explorer or in most other programs that can copy files.

Features include:

Copies directories with or without entire subdirectory structure
Optional source file deletion after copying (only if it was copied OR even if the file was skipped)
Overwrites file never, always OR only if a file is (that much) larger, smaller, older or newer than the existing file.
Or just ask the user what to do when a file already exists.

It is freeware, which means you can use it free of charge.

Download it: DirMerge.exe (for Windows 95/98/2000/XP/Vista)