My dad uses
xxcopy for his mp3 collection that is mirrored between two computers. It works pretty much just like xcopy, but has a lot more functions, and is meant to actually compete with
Microsoft's Robocopy (which they
eventually wrote a GUI for.)
He ended up writing a batch file that handled the creation of temporary network drives, then copies all the new and changed files from one computer to the other, using xxcopy. I can't remember if he has it run automatically or manually, but the task manager in Windows
I believe you have to be careful with some of the command switches, because if you aren't careful, it can be destructive if not done right (I believe it can do a directory comparison, which will delete what is in the destination that isn't in the source, and if you switch the destination and the source, you'll be deleting the source files!) But in your case, I think you'll be sticking to the /clone switch, which will clone (duh,) all of the files in the source directory to the destination.
You'd have to pay for it, since it would technically be used to commercial use, but you can test it out yourself for free.
Jam it back in, in the dark.