you need to have your eeprom and a backup of c and e then use xboxhdm and ndure to format new drive. there are tutorials all over aD if you need help
http://www.teammodders.com/forum/using-xboxhdm-to-build-an-xbox-hard-drive-t87.html that may help you. Just back up your EEPROM file to your PC, and any game saves that you may want. Or if you have space i reccomend that you just back up the whole HDD on your PC and keep it there in case anything ever happens, Trust me, you will thank me later. Softmods are funny and you would not believe how many people come on here with problems that could be easily solved if they had just backed up their EEPROM file on their PC.