Well, yes if you install a linux/xbmc "hack" on the atv 1. AtvCloners linux/xbmc image (and I *think* crystalbuntu) will allow you to use the atv 1s usb port for not only an external usb drive (or many if you plug in a usb hub) but also a usb optical drive (dvd or blu ray) .
For instance, I have three atv 1's running day and night ... one has a usb hub plugged into the atvs usb port and there is a 500 GB usb drive and a usb dvd drive running off of the hub. the atv (via xbmc) uses both the remote drive for local media storage as well as the optical drive for dvd playback seamlessly.
Fwiw: technically you don't "Jailbreak" the atv 1 (though I know what you meant) as that is a reference to hacking the atv 2 - 3's ios operating system.
Basically you hack the atv 1 the same as you do a normal computer. Much more "hackable" than either atv 2 or atv 3.