Scan your computer to see which ram it takes at http://crucial.com/
Then look up your computer specs at whatever store you bought it from for the hard drive. Theirs either ATA or SATA. All computers have ATA (IDE), but if your motherboard has SATA ports, go with that since it goes faster then ATA.
Or if you feel safe with opening your computer, see if your hard drive is either connected by a ribbon, 40 pin connector (ATA/IDE) or by a skinny cable with a smaller end.
"I think there is a world market for maybe five computers." - Thomas Watson, Chairman of IBM, 1943