The secondary hard drive i'm planning to install is the hard drive that i used on my last computer and yeah it functions well. I just want to ask, does after putting it on my new computer like the youtube video demonstrated, do i need to reformat the second drive? Because i just want to access this old drive because i have files there that i need to get. I'm waiting for your reply good guys thanks.
The fact that it has Win XP on it, OR was used under Win XP, will not cause you any problem. In fact, it helps - that OS is so recent that Win 7 will have no problem dealing with the HDD. Just as a note, though: IF Win XP is actually INSTALLED on this old drive, check in your BIOS Setup screens under the Boot Priority Sequence settings to make sure this old HDD is NOT allowed to be used as the boot drive.
In this context, "support" means simply whether your current OS (win 7) can read the File system written on the older HDD by the previous OS. The answer is easliy "Yes" - Win 7 can use any normal HDD written by Win XP. So don't worry.
As flank21 said, you do NOT need to Format - in fact, you must NOT do that because that would destroy your old data. Just mount it physically, attach power and data cables, and boot up. Your Win 7 system should find it with no help, and it should show up in My Computer with all its files ready to use.