There's really nothing special about it. OS X can have several bootable drives connected at the same time, you just pick and choose at boot time. This is especially useful for developers whon need to check compatibility with several OS versions.
The only thing that can be a bit tricky in the install is that OS X might just refuse to recognize the drive if it has an unusual format (for example it was part of a set in a RAID array). Other than that, SSD or HDD, it is really easy.
Very quick method: install the drive in the Mac Book Pro. Boot from the install DVD (if you have no DVD, see below). If the disk is recognized, proceed with the installation. Depending on the partitioning scheme of the disk, there can be small variations, but they are easy to understand and follow. If there is any hiccup at this point, go to the disk utilities menu from the boot DVD and simply remove all partitions (or only one if there are more and you want to keep data on one of the previous partitions, obviously) and proceed.
Slower method: hook the drive through any kind of adapter (USB/Firewire/dock etc...). Use the disk utilities from the currently running OS X to remove all partitions from the drive. Start the install from DVD, or eventually downloaded and kept DMG if latest versions obtained from the app store. Select the new drive as a target for installation. Then let everything proceed. Select the boot drive at will when restarting (
http://support.apple.com/kb/HT1310). One you have confrimed everythings work, swap drives.
Note that OS X will usually start to index the content of the new drive. Doesn't matter much, but is just a waste of resource.
Migrating to SSD can also be done that way
Make sure your data will fit the SSD with some margin. For example, starting from a 500GB HDD based MacBook going to a 250 GB SSD, make sure you have at most 200-220 GB used on the original drive. Make sure your Time Machine backup is up to date, Remove old HDD, install SSD, boot from DVD (or network, or even old drive then on USB, USB key... Select the option to restore from a backup and proceed.
It's really an area where OS X beats Windows in terms of convenience.
You can also clone disks from diskutil and then do the swap. In some cases you'll run into problems when the number of file descriptors is too high, but it is unusual. You might also have more complex cloning scenarios when using different versions for OS X for the boot drive and the drives you are cloning, but that probably doesn't apply in your case. If it does, stick to the same version for the boot and drive to be cloned, then upgrade the cloned drive as needed.
