If they are ceramic:
Hit them with a torch and take off whatever plates there are, process those in a cell if you have one, if not it's better in my opinion to knock off the plates anyway, if you hit them with the hammer the corners might stay and sometimes when you put your AR solution on heat, the solution just doesn't consume the gold or other PM in the corners under the plate.
After I take the plates off I throw them into a ball mill and grind them down to powder, then sift for the pins or any other larger pieces and process the powder/pins separately. If you don't have a vacuum filter you are not going to want to break them down to dust, after AR you have to filter, and if you are just using a gravity filter, it will take forever. There is some discussion if grinding them down to dust is worth it or not. I have done it a few different ways and I found that if I grind them CPU's down to small pieces, that is usually good enough. You can also check out the CrazyCrusher someone else posted about, it looks like a quick and easy way to chew through CPU's. Just search for it on the forum and you will find the post.
Using a hammer works also, I would still try to take the caps off first with a torch. When I apply heat with the torch I move the flame around evenly at a distance, pointing the flame directly on the plate. I hold the CPU with a pair of long nose pliers. You will hear the chip sound like it's breaking or cracking, you should almost be at the point where you start seeing the caps slide a little. Then either shake the cap off, or I have an old iron, iron I put in a big stainless steel pan I knock the chip on and the caps pop right off. Then you can wait for them to cool, high the chip with a hammer (remember the breaking sound when you heated it with a torch?) and they break apart fairly easy at that point because the ceramic has already weakened. You can even drop the CPU into ice water after torching so that they cool down so fast they develop micro fractures which makes it easier to break up with a hammer.
If they are fiber or transitional CPU's
Hold then with a pair of needle nose pliers, heat with a torch and shake or knock the pins off.
If you search the forum again, there is some really good information about CPU's and how to process them.
You can watch this video, posted by a well respected member of this very forum. You might be a little surprised who's video it is, check it out and guess!
http://www.youtube.com/watch?v=tQ_R8Gr26kk
Good luck
