Recently I had to replace the keyboard on a Sony Vaio VGN-NR21J. Finding a replacement keyboard wasn't too difficult (though it did mean getting a US rather than a UK version) but fitting it was rather more difficult as it seems Sony do not release disassembly instructions for their machines. As a result I had to go through a variety of guides for other Vaio's and find the bits that were the same as the VGN-NR21J to get the job done.
Remove the battery and turn the laptop over with battery compartment facing towards you.
There are two screws close together in the middle of the laptop, remove the one on the left.
Turn the laptop back over and using a small slot head screwdriver push in the tabs along the top of the keyboard which will popup.
Carefully rotate the keyboard from the top to take it out and disconnect the keyboard cable.

Although the model has now been depreciated it's worth noting that the keyboard I fitted is also for the following Vaio's so the procedure should be the same.
VGN-NR11M/S, VGN-NR11Z/S, VGN-NR21E/S, VGN-NR21J/S, VGN-NR21S/S, VGN-NR21S/T, VGN-NR21Z/S, VGN-NR21Z/T, VGN-NR31E/S, VGN-NR31Z/S, VGN-NR32M/S, VGN-NR32S/S, VGN-NR32Z/S, VGN-NR32Z/T, VGN-NR38M/S