Alright, my internet connection right now is fuzzy, but I'll try to get you all the info needed. I'll try to help you get NullDC work for you because I could find more info on it.
First of all, you may need a BIOS if your copy of the emulator didn't bundle one. This is like a rom in that it I can't tell you where to get it due to forum rules. I can tell you that a quick search of "NullDC BIOS" Will get you results. After downloading it, unextract it if it was in an archive such as a .zip, .rar, of .7z. If it's one of the latter I recommend 7zip.
Make sure you get a region free BIOS, or one that matches the region of the ISO you're using.
Toss it in the Data folder with the name "dc_boot.bin"
Next is the plugins. I'm guessing that the emulator came in a .zip or similar. Did you make sure to unzip everything and not just the .exe? They should come with it, if they don't I'll try to find you some in the next couple of days. I'm trying to research it but nothing is loading. What I could find is that you need these two things installed (If the BIOS doesn't fix the issue try this, but they're probably already installed)
http://www.microsoft.com/downloads/...FamilyID=a7b7a05e-6de6-4d3a-a423-37bf0912db84
http://www.microsoft.com/downloads/...38-DB71-4C1B-BC6A-9B6652CD92A3&displaylang=en
They aren't viruses, I promise. (That's exactly what a virus would say, but I really do promise!)
If you didn't get your copy of NullDC from here, grab it from here so we're on the same page.
https://code.google.com/p/nulldc/downloads/list
It's the bottom one. (without "NAOMI" in the title)