If as a slave then there should be no problem atall, however if its a newer and faster hard drive than original you may want to consider transfering all your info from your old hard drive onto your new one. Most new HD's come with software to allow you to do this. Although it is advisable to back up key data first and to be sure you have your operating system cd's and reg codes.
However as getting a new HD it is sometimes a good time to get a fresh start with you operating system and do a clean install.
As a comparison... (shows my primitive mind) Think of a hard disk as a huge storage room.
Formatting divides the space into little pigeon holes, and indexes every one so that they can be found later.
The operating system is the main office situated in a part of the main room, where standing orders are obeyed, and these orders on installation are placed in those pigeonholes and noted by the Office and forwarded to other places.
Partitioning if used, divides a storage room into separate parts before "formatting" each one.
Sorry if all this makes no sense, but have been itching to say it!