Upgrade Dimension 8300 Hard Drive

I just bought a WD Caviar SE 160GB SATA HD 7200RPM from Dell to install in my Dimension 8300.  I thought I was going to replace the existing 80GB, but discovered it was in good shape after ordering the larger drive.  Now, how do I install it?  I've installed other hard drives, etc., but I'm not a computer whiz kid.

I thought it would be best to install the new drive as a secondary drive, leaving the existing one to boot up from.  I bought Serial ATA 2.0 cable, but I'm told I also need a power cord for the SATA.

Any and all help appreciated.

Florabunda