1) Copy all files in the '/_dstwoplug/' into the same folder on the DSTwo 

At this time the current version is 0.51b.100825, which allows this ini OR the one that comes with  mshl2tools' 
to be in the same folder as the nds file (i.e. '/_dstwoplug/'

2) Download the latest 'mshl2tools' from http://gbatemp.net/t208136-moonshell2tools-incl-link-launcher
3) Extract the 'savbackup' folder somewhere onto your PC
4) Copy 'savbackup.nds' file into the '/_dstwoplug/' folder
5) Open 'savbackup.ini' with Notepad/Write
6) Edit the 'scandir=/' to where your 'game.sav' files are currently saved (this is USUALLY the same directory as where your games are stored
7) Edit the 'bakdir=/' to where you want your backup 'game.sav' files stored
8) Change 'BackupAsSav=1' to 'BackupAsSav=0' if you want your backups save as 'game.bak' instead of 'game.sav'
8) Save the file