Writing data to a DOT-003 DVD was done using another developer hardware piece called an NR Writer and these discs are only playable on the NR Reader version of the Gamecube.

While it does look like a regular Gamecube, the NR Reader actually features a different DVD drive that doesn't need to verify a special barcode which is present on retail discs. This also means that the NR reader isn't capable of running retail discs.

The NTSC version of the NR Reader features a switch to toggle between English or Japanese GUI. This very same mod could (can) be made on a lot of the retail Gamecubes, I remember modding my Japanese one to be able to play US games. A PAL version of the NR Reader also exists, but I doubt it features the switch, not that it needed one for that matter.

I've experienced an NR Reader in use back at the ECTS 2001 in London. Kemco was demoing their (in my oppinion) horrible Universal Studios game, and the antendees at ECTS were for some reason enjoying it. Later on I ended up with a retail copy of the game and I have no idea why people liked it that much, other than it must've been the hype surrounding a new console.

As far as I remember Kemco was the only company to have a Gamecube on display at the ECTS trade event. While I was watching someone play Universal Studios, I didn't get to play it myself as I didn't feel like standing in line, a group of people from NCL (Nintendo of Japan) showed up at Kemco's booth and were cheering when they saw the Gamecube in action, yeah cool... Nintendo themselves had decided not to have a booth at ECTS from that year and onwards, and ECTS was shut down a few years late as both Sony, Nintendo and other major publishers had left the trade event to make their own, what a shame really, ECTS was great fun.