I do want to install 2nd hard drive and it will be SATA. I am concern that my 2nd hard drive might not work because of the SATA. I don't want to format my primary hard drive. Any advice on it? I am not expert on SATA here.
Well the new SATA II-300 do have jumpers for making it SATA-150. Make sure your MOBO can handle new SATA-II 300 or make sure that the SATA has 150 support.
What do you have now?
Do you have have SATA support?
Do you have PSU that has SATA power connectors? (you can buy add-ons)
Many sata2 supported boards will support sata1 drives. There are a few Sata2 boards that will not "see" the Sata1 drives. Try 'googling' your exact parts.