i moded one myself. (actually 3 systems total so far… 2 Samsungs (MS25/MS28(i got a MS28 myself)) and 1 BenQ)
opening the case is the hardest part overall. but if you got the right tool to open it it’s not to bad… but either way it’s noticeably harder to open vs original xbox was.
http://www.modchipstore.com/Xbox-360-unlock-kit-disassemble-modchip-case-replacement-tool-16343.html (that’s the tool to open it) … i heard people have used paper clips etc to open it but i never tried that myself cause i would assume opening the very back part would be pretty complicated without that tool.
p.s. i got my opening tool from dotconsole.com for $4.99 out the door but the site appears to be down at the moment.
also depending on what drive you got in the xbox360 you ‘might’ need this… http://www.newegg.com/Product/Product.aspx?Item=N82E16815124022 (i have this myself. it’s a VIA 6421 chipset… works great on Samsungs/BenQ’s) … if you got SATA ports on your motherboard you might not need that… nForce chipset’s are generally recommended as far as ‘onboard’ SATA, if you dont have onboard SATA your probably going to need to get that card… i dont have any direct experience myself flashing Hitachi drives but i have did Samsungs and BenQ’s before.)
to make it about as easy to explain as possible… this tutorial here… http://xrl.us/oyf8c , tells you how to mod your xbox360 AND how to make backup’s of your original game discs etc… also, that tutorial aint completely up to date but it’s ‘good enough’ to tell you what to do to mod your system so it can play burned games from DVD+R DL discs (Verbatim DVD+R DL (made in singapore) are recommended)
also, if you happen to be one of the unlucky ones that got a lite-on drive in there xbox360… as of now it cant be moded for the most part although it will be by around Christmas (iXtreme v1.5 is due out around then)… cause the firmware for it is currently being made but in order to get drive key from the lite-on it will cost money (roughly 30-50 dollars) since you need additional tools to do it etc etc.
here is a easy way to tell what drive u got in your xbox360… http://tinyurl.com/6hpktl , so based on that pic as long as you dont have the ‘yellow wire’ your xbox360 wont be hard to mod
as far as your question of ‘will removing the steel chassis cause any damage to the xbox360’ … Nope. just be careful and you will be fine… cause once you remove the case you dont have to remove anything else inside the xbox360 itself to mod it… u just unplug the SATA cable from the back of the XBox360’s DVD-ROM drive and connect to the PC and that’s it. (read the tutorial it shows pretty much all of this)