The DOS xcopy command is like the copy command, on crack. Here's how you can use it to do incremental backups (only copies new or changed files).
xcopy "D:\Andy's Files\*" "I:\BACKUP\Data\" /h /r /s /e /i /c /y /d
Where "D:\Andy's Files\*" is the directory to back up and "I:\BACKUP\Data\" is the directory to back up to. /h copies hidden files, /r overrides read-only files, /s /e copies subdirectories including empty ones, /i assumes the destination to be a directory, /c continues even if errors occur, /y doesn't warn on overiding files, and /d copies only files that are newer than the destination file.