I have never really had any call to do this (no interest or JTAG box at my disposal) but OK. Naturally to do this you will need some measure of 360 hard drive access, that is covered elsewhere in depth but usually it amounts to pulling one apart and using the raw sata ports, using a datel adapter or using the MS hard drive transfer kit and all work with xplorer360 (make sure the version you are using matches the size of the drive you are working with).
DLC- when bundled with a disc comes in three main forms
1) Gears of War 2/Resident Evil 5 style- a voucher to download it in the box.
2) Borderlands and Fallout 3 style- comes as an installer on a disc and can be used many times over.
3) GTA Lost and Damned, Ballad of Gay Tony style- a game on a disc.
In the case of 2) it is byte for byte identical aside from the container format it uses (I checked with borderlands a few months back although did not take my experimentation too far in that direction).
More on 360 containers (and probably enough to make everything else I typed pointless):
http://www.se7ensins.com/forums/topic/4008...ning-explained/
Demos- for the most part if you can get them on the box you can play them.
As for game demos you can burn them to disc but when you can just flash a drive why bother.
As I am far too lazy to type it all out this evening and somebody else made pictures:
http://digiex.net/computing-section/guides...-demos-iso.html
XBLA games are the full games but for a small section (naturally changing this breaks the singing- something only a rebooter hacked 360 can dodge). See yaris patch for the initial work, indeed the only thing to have given any trouble thus far is Avatar (as in the game based on the film) DLC but that was solved easily enough.
It has been noted that some games have ways to play the full game via glitches (most notable an early version of Shadow Complex since patched but you can find the old one if you go looking).
Themes- most theme work these days is based around the JTAG stuff like freestyle dash but there is some stuff out there. You yourself gave me this link a while back:
http://spiffy360.com/forum/forum-13.html
Content/0000000000000000/FFFE07D1/00030000 appears to be the directory of choice.
Frankly the only reason most on JTAG owners go down this path is for easy save transfer (probably far easier now USB exists for normal 360s) and for title updates (I have no links/mirrors right now but xbuc aka xbox update centre is the site of choice for most.
