As a reference (with photos) I will use this article from the user who opened his 500GB version. (it slightly differs). This is not written for the purpose of exchanging the drives or making it internal forever, but only when you screw up your disk with the Firmware Upgrade 1.08a and it is dead (disk is NOT dead, disk works like charm, but the mainboard of the external device is dead, i. e. without any firmware at all). !!!And beware that you can lose your warranty when you open the case!!!
No need to identify the corner screw, because there is no such thing in the 320GB Premium version. So the step one would be very carefully (milimeter after milimeter) putting out the rubber straps off the disk. (At some points - up and down parts) you can not put it off, because it is really sticked with some kind of glue. But you can strip it from the rubber at the corners and then (the glue is every where, but not that much) when you see the hole (where the rubber was) you can put some screwdriver inside.
Step two-step five
The construction of this version is different, so you really need to use the screwdriver centimeter after centimeter until the case just pops out.
You can unscrew only one of the screws in here. That one in the left upper corner. Your goal is to save the data, so it does not matter, when you can not unscrew all the three screws.
Who cares abotu the LED, you need the disk. Leave it alone.
Step eight and step nine.
Only unscrew those four screws from the bottom. Then remove the SATA cables. (Over the sata cables is aluminium strap, so put that out carefully before).
Step ten-Step Fourteen
No need to do that. Just unscrew the four another screws from the TOP of the disk. And then you can put it out of the plastic shell. Disk is now accessible to the SATA connectors in your PC (it does not matter, that it has some kind of metal-shell-crap on it). And the disk is now fully working internal WD Caviar version.
Now save your data to another disk (and money, too, because those authorized recovery companies of the WD charge really shitloads of money for this easy crap) .
After saving the data, you can reformat it (why returning back internal working disk with your personall data). You can even use Hiren's Boot CD and run some proggy like Killdisk to safely erase all your data and then format it... (cause there is nothing easier then recover the data from formatted disk)
And now do all the steps in reverse. First of all put that rubber strap on the plasic shell where the disk is seated - it is easy (sometimes little tricky, but nothing impossibble). You can use the screwdriver before and screw all those eight screws (from the top and the bottom) and the ninth little screw for the LED control.
Now only click the case back on it and you have a dead non working external MyBook again. It is much easier to put that rubber straps on before clicking that case back on it.
Now you can try your luck, if the reseller grants you exchange of the disk for the working one (because you void you warranty with opening the case).