Always have system off before swaping cables and make sure that you are grounded.

One method

Open case -> disconnect Optical drives -> Attach 20 gig drive to end ribbon cable from Optical drivers and power connection.

Boot system -> allow windows to find new Hwd, Re-boot may be needed, Use Wnds explorer to Drag and Drop files to new drive. When finished re-connect Optical drives.

Another method

Change jumper on 20 gig drive to cable connect. Jumper postion is marked on the top of the drive and the jumpers are located beside the 40 pin ribbon connector. Attact using center connector of ribbon cable going to new drive.Boot and use Windows Explorer to transfer files.

Purchase an USB external enclousre.
Attach old drive to device -> plug in after boot -> allow Windows to find and transfer files.