Have you set up the HDD partitions and put on the retail files yet? Just asking so you don't put the new drive in and then realise that you have to remove it and set up the drive. I know people who have done that.
You should be set then. I thought it'd be best to make sure because it's something that happens alot to people new to xbox hardware mods. A friend of mine tried upgrading his HDD and didn't lock it again and he didn't back up his EEPROM and he lost his BIOS and everything, so now its screwed up and I'm fixing it.