If you purchase Win 10, then yes.
If you Upgrade your existing Win 7 license to Win 10, no.
You don't need to do anything special.
There are 2 ways to do this, depending on how you want to choose what OS and drive you wish to use:
1. Choose in the BIOS at start up:
For this, you disconnect your existing Win 7 HDD
Install Win 10 on the new drive
When you power up, override the BIOS boot process, and choose which drive
or
2. Choose from a Windows menu
For this, you leave the Win 7 drive connected
Connect the new drive
Install Win 10 on the new drive
If it all goes OK, you will be presented with a menu like this when you boot up:
(don't mind the words "Technical Preview". This is an old image from when Win 10 was still in beta.)
Caveat with method #2. If you later remove that Win 7 drive, bad things will happen. As in no boot for you.