First tell us what kind of HDD is in your 'old' computer (Company, model, size, PATA or SATA) and if it was a boot drive (has an OS on it as well as data).
Then tell us what your present computer is (Company, model, what available internal ports you may have, and what external ports on the back as well as USB ports that are available).
Then one of us can give you clear instructions as to how to copy your old data over to either a new HDD, or USB flashdrive. And if you will need any additional "interface" device to connect the older HDD to the new computer.
We don't necessarily need All that info ^^^
It boils down to what connector is on your drive and what you are connecting it to. To make things simple, take a look at this, which will connect any type of drive to a computer via USB - http://www.newegg.com/Product/Product.aspx?Item=N82E168...