When considering Irrlicht on the Xbox multiple factors come into play. The most vital factor is what SDK to use. There are two main options: OpenXDK (www.openxdk.org) or the official Xbox SDK.
First, let's talk about OpenXDK. To obtain OpenXDK you can simply download the source files for free from the website. Then, you need to compile it using gcc (not Microsoft Visual Studio or anything of the like). If you can't use gcc then you can use the original (LIMITED) version of OpenXDK that the current one is based on found here: http://www.caustik.com/. Released November 7th, OpenXDK v 0.05 has support for sound (44 khz mono) using one format, and the graphics side of things uses SDL. So, if we wanted to get Irrlicht onto the Xbox using OpenXDK we would need to create a CIrrDeviceXbox using SDL, and port all DirectX and OpenGL functions to also SDL functions. Quite a bit of work, but possible. Then, we could compile the xbe for Irrlicht very easily, and it could be running on the Xbox.
Our second option is, as mentioned, the official Xbox SDK. I just wanted to give some information not about it specifically (because look at any game released on Xbox today and you can see what it can do) but HOW you would get it. First, you need to be a profitable, official company (Ltd. Inc. Co., etc.) with at least 4 successful published games under your belt for any platform. Then, on top of that, the official Xbox SDK is estimated (counting in developer tools, hardware and software) to be about $40,000 USD. The official Xbox SDK uses DirectX, and as such it would be quite easy porting Irrlicht to the Xbox this way, with a few minor changes as to how it handles printf'ing and such. But, being that the person who does this would need the aforementioned tools, it is virtually impossible (expecially in an open-source community).
So, you should now realize that unless there is someone sitting around who is part of a big company with the official Xbox SDK (very unlikely, but possible), to port Irrlicht to Xbox we need to go the OpenXDK route and make an SDL device. In writing this, I just wanted to provide some information as to how we can do this, and how we should do this. Now, the real question is who wants to do this?