RetroArch for Windows 98 SE / Windows ME / Windows 2000 has just been released! Note that this will require cores specially made for it, and as of now there are none, so just consider this a pre-release for now!
Users should note: this is taking no time or resources away from the other stuff we are doing. Supermodel and PPSSPP cores are still being worked on, all our other work is still ongoing, so to repeat – this is not coming at the cost of other development!
Note that for these old operating systems, you might want to consider using the GDI video driver for optimal performance instead. Menu support is still premature though; XMB renders but with no textures and with dithered graphics, so for all practical purposes, the Direct3D driver is still the way to go here (with RGUI).