At present the slim 360 can not be hacked in any real way but the others are still possible.
JTAG- the best way to hack a 360 (assuming you can live without live- see another post around here shortly for more on that though). All 360s that have been updated past the August 11th 2009 can not have it done and those there made from mid June 2009 or saw a repair shop in a similar timeframe can not be hacked either.
It is a bit outdated but covers the essentials:
http://docs.google.com/View?id=dnfmv5h_186pp2zddm
DVD drive- aside from the slim all models of DVD drive can be hacked (this might change as some later models are built with slim drives but nobody has seen that yet).
Some of the latest models (late last year) known as a the liteon 8v2 and and 9 series (started appearing in late August 2009 if not a bit later) will take a bit more effort (you will have to fiddle around with the drive mainboard) but not that much.
Other 360 drives other than the 7 series liteon (which will require a probe* or the same method used by later model drives) can be flashed with nothing more than a compatible sata chipset (VIA 6421 works for all and later model Nvidia for most of them other than that) and 10 minutes work if you are slow (or have not done it before).
* homemade version
http://forums.xbox-scene.com/index.php?showtopic=668247 and you can buy them in most mod shops.
http://www.jungleflasher.net/downloads.html has a nice tutorial and doubles as the go to choice for a windows based 360 drive flashing program.
At present for no hack should you have to touch a modchip and indeed never use them for a drive hack.
As some stuff for the 360 is dubious under various copyright laws Xbins is the place to look for 360 related stuff, it is an FTP/IRC thing but an automated tool exists in easy xbins:
http://www.360mods.net/index.php?name=Down...tails&id=29
JTAG 360s can not be used on live, DVD hacked ones can but once a year or so MS does ban users with hacked DVD drives (it is a bit more involved than that- I reckon if you settle for it will work but do not expect to get away with it forever especially if you do not play it safe (using unchecked/hacked ISOs and playing them before street dates) that will be a good mindset).