Welcome to HBH! If you have tried to register and didn't get a verification email, please using the following link to resend the verification email.
Changing Harddisk
If it's old it's probably connected with an IDE cable. Most motherboards support this. All you have to do is open up your computer and check. If you don't know your way around you might want to ask someone to help you.
Here you can read up on the various interfaces. http://en.wikipedia.org/wiki/AT_Attachment