Well there are a few ways of doing the softmod on the Xbox. There is some old game, that allowed you to use a flash drive to load extras. Someone saw this as a weak spot, and allowed a file that would kill the xbox, and boot it to linux. I think.
Ok, this is how sorta, step by step:
Buy/Rent the game MechAssault. Make sure it is the original copy. Microsoft fixed the newer copies so the exploit couldn't be used. The news say, "Platinum Game", or "Platinum Hit" or "Game of the Year". So your copy must have the Product ID or Part Number X08-82261, X08-82262, or X08-82264. Make sure to check the disc too, because sometimes they put different discs in different cases. I also read that the inner ring of the disc should be lasered MS02301L, and NOT MS02308L. You can also use Splinter Cell, or Agent Under Fire, but are not suggested due to lack of reliability.
Get an xbox "Action Replay". It is about $20 to $30. Looks like this:
You will also need 3 downloads. mIRC, FlashFXP, and of course WinRAR. Who doesn't have WinRAR?!?!?
Then actually mod it! Download Krayzie's NDURE exploit. You can find it on many torrent sites. It is about 36Mb zipped. Also download Xbox Media Center also called XBMC.
Now put them on your XBOX! Install Action Replay on your PC. You should see three columns in the Action Replay window. Drag-and-drop the ZIP file labeled udata.zip, located at "\Krayzie Ndure Pack\MA\MA save" from the downloaded Krayzie file into the center column labeled "PC database". Now scroll down the list until you see "MechAssault" and a child item labeled "Run Linux". "Run Linux" is the title of the game save that you will load up within MechAssault. Drag and drop this file from the "PC Database" column to the "Memory Card" column on the left. This process can take several minutes as the memory card is written. A dialog should tell you when it is complete.
Before you actually start putting the modded memory card into the XBOX, delete all the saved games and xbox live game saves for MechAssualt.
Put your copy of MechAssault into your Xbox and it should load up. From the main menu in Mech Assault select the option labeled "campaign". Now, you should see the familiar gamesave title "Run Linux". Load this gamesave by highlight it and pressing "A".
First, select the option to back up your EEPROM (you might have to select it again in a subsequent menu), then install the softmod. The installer will guide you through the install procedure and keep you updated on its progress. Once the mod is complete you will be prompted to reset your Xbox and remove the game. The installer will then make a shadow copy of your C drive. After reboot, you will now have a modded Xbox!
Powering on your Xbox without a game loaded should now bring you to the EvolutionX dashboard.
It is now possible to install other software and files because you now have access to your Xbox's hard drive through FTP access over your network. Cool, eh?
If you haven't already, you need to connect your Xbox to your network (or at least your PC) so that you can get FTP access. If you have a typical home network with a router, then your Xbox should be accessible by an IP address assigned by DHCP on your router. (Read this if you don't have a home network and will have to connect your Xbox to your PC using a crossover cable).
Determine your Xbox's IP Address by going into the "settings" section in EvolutionX where it should be listed. You can check to see if your Xbox is available on your network by "pinging" this IP address from the command prompt on your PC.
Go to the location on your PC where you download your copy of the XBMC .RAR file. Using WinRAR, extract the files to your PC.
Start FlashFXP and navigate locally to the location where you extracted XBMC on your PC. Now, open a new FTP connection to your Xbox. Enter in the IP address from step 7.1 and username: xbox with password: xbox. You should now be able to get access to the Xbox's directory structure.
Navigate to /E/Dashboard/ on your Xbox. This is where EvolutionX is installed, so to have XBMC replace EvolutionX, you simply have to copy the XBMC files to this location, overwriting the existing files. Now select all of the files from XBMC that are located on your PC and transfer them to the /E/Dashboard/ directory on your Xbox. This will take several minutes, so please be patient.
Once this is complete and you power cycle your Xbox, Xbox Media Center should start up.
You can configure Xbox Media Center from within the dashboard itself or the setting can be modified directly in the XboxMediaCenter.xml file located in the root of the application directory on the Xbox.
Use the FTP program to copy all your files and such over too!
**Please note that I wrote some of this and found other parts scattered throughout the web, and in txt files I have collected (don't ask!). Not all original work here!
I see someone beet me to the punch with the short and sweet way! Damn...