Simply S-OFF your DS, install the app and run it.
You will get the following message:
"Not sure what happened here. Either the exploit failed or the reboot failed. Please reboot manually and see if you have SuperUser!"
Reboot your handset manually and you should have SuperUser installed with root access. However you will need to install busybox from the market manually or from within Titanium Backup.
Happy Rooting for those with S-OFF.