Okay, so you're going to want to make a clean 2GB, 1GB, or 512MB virtual SD card (if you have a virtual one this size already you can just delete the files off of it and you'll be good) and open it up in WinImage. Once you've done that you're going to want to go to Image > Inject Folder. Navigate to your extracted Brawl Minus folder (the one that contains the apps, codes, and private folders), select it, and inject that folder. Wait for it to complete, save it, and you'll have a working SD card. Next you're going to want to grab a working version of gecko. This is really easy: use boot.elf from your Minus download. Now make sure your Dolphin settings are correct (SD card inserted, Brawl is default ISO, whatever speedups and compatibility settings you need are good, etc) and your virtual SD card is in the right location and when you open up boot.elf Dolphin should launch Gecko with a Minus theme. Launch game (and possibly check to make sure AXNextFrame is the hook type, it should be by default though) and you should be playing Minus on Dolphin.