I'm not exactly a computer expert, and I need as much help as I can get. However, I may be able to give you some help with this one.
I am assuming that this is the first addition to your original system. Then, you should be considered about 3 things: jumpers, the IDE cable (flat, wide grey cable) and 4-prong power connector allignment. Make sure your AC power is disconnected when doing any hardware work on your computer.
First, you should put the jumpers at the back of the hard drive to "slave" (Depending on the manufacturer, you need to put it on "CS" or "CSEL" (cable select)). A good way to tell is to look at your 1st harddrive. If it has the jumper at "CS" then you want to also put your second hard drive to "CS" - this is common for compaq (I have 2 Compaqs and they are both like this). By putting it in cable select, you are allowing the computer to figure out which hard drive it should use to boot up the computer (I am assuming that the second drive will not have an operating system installed). If your 1st drive has "master," then put the second drive to "slave."
Second, when connecting the IDE cable make sure the red-lined side goes towards the 4-prong power connector.
Third, when connecting the power connector, make sure the red line goes towards the IDE cable.
Then, start up the computer and open your "Windows Explorer" (not MS explorer) and look under My computer. Your new drive should show up. Then, you can format the drive with the disk that came with the drive. Actually, see if your computer allows you to use the drive without formatting. I think depending on the operating system, you don't need to. Okay, now we are getting into the area that I am not too good at. See if it works. For further comments, you need the help of other friends here.