Yo dont flashg the bios through the cable, you make a CD-RW with the bios file on it, and boot up into the flashing bios (usually 'bank b' on the mod chip switch). As said above, all the tutorials are on xboxscene.
Once you've flashed and installed a new dashboard (I'd suggest the Evolution X Dash), then you can connect to your Xbox using an FTP client on the pc and drag and drop files to the xbox hdd....