First, go to your evox setup and click "Backup"...once it's done the backup, use Filezilla, or some other FTP program and FTP from your PC to your XBox. Browse to the C drive on your xbox, you'll see a folder called "Backup". Inside this folder you should see "eeprom.bin", "hddkey.bin" and a few other files. I suggest FTPing the whole folder over to your PC. Once you have the Eeprom, you should be fine. That's really all you need to build a new HD. If you want, you can FTP the whole C and E folders, that way you'll have basically your whole xbox backed up.
Once you build a new xbox hard drive (look for tutorials on the program 'xboxhdm'), that's what you'll use to build your new HD. You'll need the Eeprom file once your HD is built. xboxhdm uses the eeprom to lock the hard drive so it's usable in your xbox. REMEMBER! It MUST be YOUR Eeprom from YOUR xbox!!! Each Eeprom is different and the bios will know if you lock your hard drive with the wrong eeprom! If you do this, your xbox will not work, it will just give you a hardware error.
Hope this helps. I'm no pro at this as I'm having issues locking my new harddrive myself, lol, but I've done this 3 times with no problems and once (right now) with some difficulty locking the drive. If you need more help, I can tell you what I know