Ugh... buying the SC for emulation, as I said before, is kinda pointless. I mean it's great that you have another device in case the EZ-IV fails, but the emulation thing is silly simply because the built-in emulators are nothing more than built-in versions of publicly-available emulators, and they're often out of date.
Here's what happens normally, for all other cartridges including the EZ-IV. You download the emulator (using Goomba Color as an example). You run the rom builder, which combines the goomba.gba emulator core with the GB/GBC roms you select. You receive an output *.gba file with everything combined, then you put it on your card and run it. Maybe involving the EZ-IV patcher, I don't know (see the previous link I posted). In the case of Goomba Color, it's as simple as doing a command-line entry of "copy /b goomba.gba + game1.gbc + game2.gbc + game3.gbc outputFile.gba" although for other emulators like PocketNES, there's a tiny bit more magic done behind the scenes that the PocketNES Menu Maker does. It's still essentially nothing more than a binary combination of files.
On the Supercard, you can launch *.nes and *.gb/*gbc files directly from the miniSD card, but all that it's doing is replacing that "copy /b" command and the functions of the PocketNES Menu Maker in realtime. Internally, it adds the rom file to the end of whatever version of the emulator it has built into the firmware, and launches it.
The key point is that the Supercard doesn't have special versions of the emulators or anything. It just has built-in versions of PocketNES, Goomba Color, PCE Advance, and SMS Advance. Only the Supercard DS:TWO has anything in the way of original content, with its GBA emulator for the DS.
One final note: know that as a 16-bit system, almost every single program for the GBA
must be less than 32 MB to execute, including emulator compilations. So you can't put the entire NES library into a single *.gba file, for instance. The only exceptions are a few 64 MB "GBA Video" releases that use some unknown-to-us form of bankswitching. On the Supercard, all GBA games are loaded into its 32 MB of PSRAM and executed, and that takes a few seconds, moreso if the *.gba file is larger. On the EZ-IV, files under 16 MB can run from PSRAM in the same way, while anything larger must be loaded to NOR flash. NOR flash takes a lot longer to write to, but it doesn't disappear after powering off like with PSRAM. See
http://www.pockethea...le=NAND_and_NOR for an explanation; it tells it better than I can here. Before things like the Supercard and M3 and EZ-IV came around, NOR was the de-facto standard for all GBA flash carts. It was also expensive. My Flash2Advance Ultra cartridge for instance is purely NOR, and at the time that I bought it, paying $100 for a cartridge with 128 MB of storage space was a steal.
Other GBA things: look into GBA GSM player by Tepples (and his other works) if you want to use the GBA as a music player. The GBA is too weak to decode MP3 files in realtime, so you must use either GSM Player or Music Player Advance, which I personally found annoying to use. Both compress the files and thus have significant audio artifacts, but they work. Also look into GBA JPEG Viewer for image viewing and METEO for very limited video viewing (5-25 minutes depending on the quality, limited by the fact that GBA files can't be larger than 32MB as I said earlier). I can provide a link to the latest version of METEO if you're interested, as it's not widely known in the Internet.
EDIT: I might as well go ahead and link it, even if you don't care. The website is gone, but Archive.org has an old version.
http://web.archive.o...php?p=utilities
EDIT 2: oh wow, reading that page again, I forgot about Boot-O-Matic Advance. It lets you soft-reset to your flash cart's loader in many instances. Quite useful. I run most of my homebrew GBA files through it before putting them on my cart.
Bunjolio's mother that he's swearing]