I recently had occasion to change the hard drive on work's Sony Vaio VGN-A497XP. Google turned up a useful guide at here, but the original page is now gone and we're left with the archive on the Wayback Machine.
I followed those instructions. Here's my experience.
The same case is used on the VGN-A417S and VGN-A417M. The case for the pages I followed are for a VGN-A197XP, so I suspect this case is common for all VGN-A type Vaios.
Begin work with the laptop close and lying upside down.
First remove the battery.
Next remove all the screws visible on the underside where the screw hole is marked with an arrow ⇒
. Be sure you know which screws go where when it's time to put them all back. I laid them out in a pattern reflecting their positions in the case.
The next stage is to remove the keyboard. Turn the laptop the right way up and open it up so you can get at the keyboard.
The keyboard has a couple of small catches at the front. Here you can see a pair of small screwdrives being used to push them back.
Then lift the keyboard up from the front, being careful not to strain the ribbon cable.
Gently lift the ribbon cable connector and ease the ribbon cable out.
Remove the keyboard and place it out of the way.
Next remove the two screws holding the top cover of the laptop base. The screwdrivers show where they are.
Now very carefully ease the two small ribbon cables on the top cover out of their connectors. The screwdrivers show the location of the connectors.
Now you can ease the top cover off. It is clicked in place along the screen edge. I just lifted it gently from the front, wiggled and persuaded until it came out.
The hard drive assembly is at the bottom left. Undo the six screws holding it in.
Fold the board covering the drive out of the way (you can do this without disconnecting anything).
Gently lever the header board up until disconnected. You will then be able to remove the drive + header board assembly. Ease the header board off the drive. Unscrew the drive from its casing, and replace it with the new drive.
Reassembly is, as you might expect, the reverse of removal.
Ease ribbon cables carefully back into their connectors. After replacing the top cover, press it firmly at the back by the screen; there should be a few clicks as it pops back into place.
Thanks to StefanVGN-A197XP for the original instructions.