For lapping...
Buy 200grit, 400grit, 600grit, and 800grit industrial wet/dry sandpaper or get as near to those numbers as you can. Above 800grit will get you a more mirror finish, but extensive testing results I read on another forum showed that above 800grit yields less then a 0.5C difference in temps, usually unnoticeable. Do it if you want to, but not worth it by any stretch of the imagination unless you want to take a picture of your mirror finish to hang on your wall.
Get a bucket of luke warm water and add a drop of dish soap. Wet the sandpaper and the bottom of the heatsink/waterblock thoroughly and slide it across in one direction without putting too much pressure on it. Let the weight of the heatsink/waterblock do the work. When you get to the end of the paper pick up the heatsink/waterblock and bring it back to the beginning of the paper. Repeat. Some suggest going in circular motions or alternating your directions, but anyone who works with tools will know that going one direction the ENTIRE time will yield the best results. Switching directions will cause uneven areas. Be sure to wet and change the sandpaper regularly and rinse the heatsink/waterblock regularly.
A good way to know when you can move up to the next grit is to make an X on the bottom of the heatsink/waterblock with a permanent marker and lap until it's gone. Then move up to the next grit. Once you finish with the 800grit and get rid of the X completely you should rinse the bottom thoroughly and then use pressurized air to make sure you get all the particles out of the minute spaces. Now you're ready to apply Nanotherm PCM+ and put it on your CPU