Replacing Macbook Pro HDD & Installing Operating System
As far as I understand, you have a running Macbook Pro with an ageing HDD and want to upgrade/replace the current one and also move to Mountain Lion in the process.
I can suggest you the following.


Purchase a USB casing for your new HDD and temporarily convert it to a USB Drive. These are not too expensive and you'll see more benefits in the end.
Connect it to your current system.
Run the installer on your machine and choose to install on the connected USB drive instead of your current system disk.
After the setup is done, remove the HDD from USB casing and replace the system disk.
Use the system disk in the USB casing to have a high capacity backup drive.