I believe to play your DVD iso's, you will need to perform more advanced softmodding.
From my GeeXboX link:
GeeXboX for Wii (IOS) is basically the continuation of previous 0.1alpha releases and has to be launched by, preferrably, HBC or other similar homebrew loading methods. This version does not support native wifi or DVD; does not support USB 2.0; does not support front SD slot hot-swapping; does support returning to HBC.
GeeXboX for Wii (MINI) is basically the IOS version modified to take advantage of MINI firmware and has to be launched through MINI, i.e. manually from Bootmii GUI or automatically by replacing ppcboot.elf in bootmii folder. This version does support native wifi (currently at a rather low speed); does support USB 2.0; does support front SD slot hot-swapping; does support native DVD; does not support returning to HBC.
I didn't use the MINI version since I didn't want to get that deep into softmodding. I believe Aether boots DVD iso's and plays them with the Wii, but I don't know what he uses.