In order to use the 3-n-1 you must have a DS and a slot-1 card, I dont think there is any other way to use it. You load the GBA roms, onto the slot - 1 which will temporarily transfer it to the 3-n-1 for use. lastly, edit the previous post instead of bumping it. Thanks
Depending on what slot 1 flash cart you're using you might not need it. The Acekard2 (with AKAIO) and EZFlash V have in built in support for the 3 in 1.