First off, I meant to use /d not -d. Sorry, dumb error that. I'm not sure what you're using it for, but here's what I made a batch file for.
When I insert my MicroSD card, the menu that windows gives has the top option of backing up my saves. What it does, it copies every *.sav file on the card to a directory on my computer. If the file already exists, it only overwrites it if the save on my card is newer than the backup on my computer. Otherwise, it skips it.
Here's what's in my batch file:
xcopy /S /I /Y /D \*.sav C:\NDS\R4\Saves\Joe
This might help for switches and such.
http://support.microsoft.com/kb/289483