Installing Second Hard Drive?

ok i ask this question about 30 mins ago "Ok i have a 180gb hard drive on my computer right now, and i wanna install another hard drive that's 120gb can i have two drives on a single computer and how do it?" see the thing is i wasnt specific enough my computer is fairly new it's about a year old unfortunately with technology advacing at such a fast pace upgrading can get confusing. i have a gateway 507 gr whatever that is... and the hard drive that is installed and im just qouting the manual serial ata drive or just ata not sure. the hard drive that i purchased is western digital caviar SE. on the drive it says it's a IDE Drive. i tried installing it but that gray cable that goes into the slot is being used by the disk drive is there another solution? another thing if i install this second hard drive do i lose any info on my current hard drive?.