A useful program to do this is robocopy from Microsoft. This program is part of the Windows Server 2003 Resource Kit Tools. The tool is used from the comand line (Dos window). http://en.wikipedia.org/wiki/Robocopy

Download it here: Windows Server 2003 Resource Kit Tools

RoboCopy GUI is a graphical front end for robocopy.exe and can be downloaded from here Download.  

(There is documentasion once you install the Windows Server 2003 Resource Kit Tools. or click here)

Example of  robocopy usage:
robocopy  o:\  D:\2009-06-28_500   /Mir    /R:4  /W:1      /np  /log:o:\roboCopy_log_file.log  /tee  

It took approx 17 minutes to copy 343 Giga Bytes ! (Remember it only coppies a file if no file of the same size and date exists in the destination directory)

  Started : Sat Jul 11 22:00:02 2009
                Total    Copied   Skipped  Mismatch    FAILED    Extras
     Dirs :     54412       105     54307         0         0        38
    Files :    242266      3155    239110         0         1      7030
    Bytes : 343.631 g   6.518 g 337.112 g         0         0   8.629 g
    Times :   0:16:40   0:06:46                       0:00:04   0:09:50

    Speed :            17225112 Bytes/sec.
    Speed :             985.628 MegaBytes/min.
   Ended : Sat Jul 11 22:16:43 2009


Automating File Copping
1) Put the rorbocopy comand in a batch file
2) Use "Start -> All Programs -> Accesories -> System tools -> Scheduled Tasks" to schedule the task.

1) Removed long path names by manualy editing the directory names to shorten them.
2) Found Long Paths by one of thee methods (2 programs) and Dos dir comand:
                                Cut-Long-Names_v1.6.exe
                                pathscanner.exe
                                dir   s:\   /s  /b  |  sort  /+256  /r  > LongName.txt