Hard to answer. Modchips are very forgiving about what needs to be on the harddisk. Softmods are based upon exploiting the M$dash. So, you need a working dash to exploit.
I would suggest to backup the xbox eeprom and transfer the eeprom.bin to your pc.
Next, I would ftp the xbox E and F contents over to your pc so that you have a backup on another disk.
After that, you could use the xboxhdm package together with the kingroach ndure softmod to prepare your harddisk for a softmod. You can extract a rescue iso like slayers or AID to have the original m$dash files. I use the Qwix program to extract xiso's.
Once the C partition contents of the disk are altered, you can lock the harddisk.
You will need a pc with 2 ide connectors for xboxhdm. If your pc only has one ide connector, you could try the xboxhdm2 package.
You could also prepare a folder on your pc with all the needed files and folders for a softmodded C partition, and ftp those over to your xbox harddisk. You will need to lock the harddisk before you can boot from it with the modchip disabled.
regards.