Solder the TSOP points, then use a boot / rescue / install disc (e.g. HeXEn, Google Heimdall's Xbox Engineering Disc, burn it to DVD-R at 4x or slower) to flash the BIOS and set up the new dash.
Once that's done you can use HeXEn to build the new hard drive. Install the drive, boot with HeXEn, set up the new drive.
Alternatively you can do the flashing manually, using Evox or one of the Raincoat flashers.