Your two drives will never be on the same partition. However, there are a few things you can do.
- Usually, the motherboards come with two SATA slots for hard drives. If you are using a desktop PC, you could add the second HDD inside the main CPU case and hook it up via the regular SATA cable.
- If you have the original installation DVD for your Windows 7, I would personally recommend that you should format the new hard drive and make that your primary partition, and then add the older HDD as your secondary.
- If you have a laptop, however, you may not have the space to do #1 above. Try #2, and then attach the other hard drive using an external HDD case via USB.