1. Make sure you plug into a SATA port on the motherboard that is rated for 6 GB/s
2. If you want to replace your HDD (higher capacity newer tech HDD) then you need to 'clone' the present HDD. I did this to a laptop and to two desktops very successfully using Apricorn's Drivewire. Details here: http://www.apricorn.com/product_detail.php?type=family&id=39
This is available at most computer stores as well as directly from Apricorn. Very helpful folks!