My slot 1 is a Supercard DSOne, SDHC and I just got the 3in1 for my slot 2. I got GBA ExpLoader version 0.57, put it on my slot 1 (nds patches automatically), Put the roms in a GBA folder, and these are the steps I've taken so far:
Turned DS on
Ran ExpLoader (it's in PSRAM mode. I want to be...