XEXMENU for playing iso's off of your external usb hdd:Video for burning the xexmenu live cdInstalling XEXMenu as a live cd
Once you install XeXMenu make a folder on the root of your external hdd (which should be formatted in fat32) called "games" (without the quotes). After that you can download a program called "xbox image browser". Extract the iso to your games folder (using Imagebrowser). Make sure you delete the $system update folder from the games directory or else you could blow the e-fuses and lose your jtag exploit for the future.
Snes360, Genesis360 and MAME360 for playing roms (get at usual places). If you need help installing the emus I would just use the search function in the forums.
As far as I know there is no media player for jtag'd consoles. But I could be mistaken?