how do I get old data off a spare hard drive?

Answer 1

If you are talking about transfering data from an old hard drive to a new one....

With the computer turned off, disconnect the power cord and ribbon cable from the back of your CD drive, and connect them to the spare hard drive.
Restart the computer
It should add the spare hard drive as another "letter" on your computer - D: or such.
Open a "my computer" window to show the spare drive. Open another to show the c: of your computer.
Drag any data you want from the spare drive to the c: drive.
When done, power down, remove the spare drive and reconnect the CD drive.

Answer 2

if you are talking about recovering lost data you can get data recovery software like r-tools but if the data is there all you have to do is install the HDD in your PC make it the slave HDD and access all your data thru the other HDD