You should be able to access the config ok. Just go to the Wii channel menu and select the disc channel (but don't have a DVD inserted) and click eject 3 times. Eventually it'll look like a gamecube game is inserted. Then select this and it'll go to the config.
The JTAG cable is for updates, i suggest it's installed with it hanging outside the back of the Wii where the USB ports are. You'll never need it unless something changes with the Wii menu's and it needs to be sorted for a new game, or new feature of the Drivekey. I've not installed my JTAG although i wish I did with this bloody NSMB issue I need to update it with (i got V1)